Amazon asks, &39'What if you switch&39' Apple doesn&39't.

Not too long ago I wrote a post about the iPad 2 as an e-reader. Recently, I read through some of the comments and noticed one that caught my attention.

"I refuse to buy books from Apple that can only be read on Apple devices," declared a CNET reader who goes by the handle GSOgymrat.

I pulled that quote out from a longer comment (see full version here), but I thought it was pretty telling. One of the big things that Amazon and Barnes & Noble have been playing up is the fact that their apps--and your digital book libraries--are device agnostic.

Amazon's app motto is, "Buy once, read everywhere" and it ran a series of What if you switch-themed TV ads promoting the concept. Barnes & Noble's app page screams: "Read what you love. Anywhere you like." It doesn't have quite as many app choices as Amazon, (B&N is missing Windows iPhone 7 and Amazon has announced a Kindle app for HP's Web OS), but it's pretty close. Kobo, too, has a set of apps for a wide variety of devices.

iBooks, however, is relegated to Apple iOS mobile devices (we assume an OS X version is in the works), which is fine for all those people who just own Apple devices, but might seem limiting to those who would consider the possibility of dabbling in other platforms.

While I haven't bought any e-books in the iBookstore (OK, one, but buying your own book doesn't count), ironically, I have bought several books from Apple--as apps. The books I buy from Apple are almost all children's books--and they're cheap. Like a lot of other people I picked up a bunch of Dr. Seuss books during the sale celebrating Seuss' birthday. They all cost $1.99 or less. For those prices, I figured what the hell, I have an iPad, iPhone, and iPod Touch, my kids are pretty covered. But I've had a Galaxy Tab out on loan from Samsung and now I kind of wish I could put those books on the Tab without having to rebuy them. I can't. At least with the Kindle or Barnes & Noble apps, I can shift my text-based e-book purchases over to the Tab.

Today, Amazon's Kindle Store leads the pack in terms of the overall user experience and selection. Barnes & Noble isn't far behind and Apple is Apple and after a flashy but sputtering start in the e-book realm, it's starting to get more serious. Random House is now onboard with all its titles, so the iBookstore doesn't have the big selection hole it once did. Also, I expect the overall shopping experience will improve as Apple puts more resources toward iBooks now that it's taken a greater interest in the e-book business (if you remember, back in January 2008 Steve Jobs famously told the New York Times that, "The whole conception [of the Kindle] is flawed at the top," because "People don't read anymore.").

As the iBookstore continues to improve, so, too, will competing e-book stores, and Amazon obviously needs to get into the color game if only not to cede too much ground in the ever-growing interactive e-book genre to Apple and Barnes & Noble, which has launched its Nookkids platform for the Nook Color (and as an app for the iPad). It's already taken a big step forward in that regard by launching its Amazon Appstore, which has those same Dr. Seuss books I bought in the Apple App Store and plenty of other picture books.

Right now, it's very unclear who owns what percentage of the e-book market and whether e-book apps are counted as e-books or not. Last year, Ian Freed, an Amazon vice president in charge of the Kindle, told me that Amazon had around 70 to 80 percent of the e-book market. More recently, during Barnes & Noble's last earnings call, William Lynch, the company's CEO, said Barnes & Noble had captured 25 percent of the e-book market. That doesn't leave much room for Apple, but it's probably in third place right now (if you count all the e-book apps), with Sony and Kobo rounding out the top 5. The Google eBookstore is just a tiny sliver of the pie.

iBooks will grow simply by Apple selling more iOS devices. The one advantage it has over competing e-book stores is that you can use your iTunes account to buy e-books. You can argue over how significant an advantage that is, especially since a lot of people already have Amazon accounts they can use to buy Kindle e-books as soon as they download the Kindle app onto any device. But the convenience of Apple device owners working off one single account certainly has its appeal and shouldn't be underestimated. (Side note: One of Google's stupid moves with the Android Market--and why a lot of people just download free apps--is that you're not required to sign up for an account and input a credit card number to download something for free. As a result, many people don't bother setting up an account. In contrast, Amazon's new Android Appstore requires you to have an Amazon account to download free apps, which then puts you one click away from paying for apps.)

The iBooks shelf would look good on other tablets and smartphones.

But iTunes account conveniences aside, you're still left with the restriction of not being able to move your library from device to device. That's certainly what's kept me--and a lot of other people--from buying books through the iBookstore, even if those e-books look and cost the same anywhere you buy them.

And that's why Apple should make the bold move of creating iBooks apps for Android, BlackBerry, Windows Mobile, Web OS, and any other platform where Kindle and Barnes & Noble are playing.

Sadly, I have my doubts Apple will take this route. Instead of letting the wall down, it may instead choose to build it up. A lot of folks are concerned over what will happen on June 30 when Apple will supposedly force e-book sellers like Amazon, Barnes & Noble, and Kobo to modify their apps to make their wares purchasable through Apple's in-app purchasing API, which pulls out a 30 percent cut of the sale for Apple. Today, Amazon and others avoid paying Apple anything by sending users to a Web site outside the app to make purchases.

If Apple sticks to that 30 percent number, it will make it very difficult, perhaps impossible, for e-book sellers--and other content sellers--to continue under those terms because Amazon is currently taking its own 30 percent cut on sales from publishers (a more palatable number may be 30 percent of Amazon's 30 percent profit). Apple, of course, is the gatekeeper of its devices and has every right to call the shots.

Whether it gets hit up with an antitrust lawsuit is another matter. But Apple built the platform, it sets the rules, and if you want access to all its millions of users, you have to play by its rules or take a hike. However, when it comes to its own e-book app, it would do well to loosen up a bit.