Facing unrelenting competition from Apple's iPad, many rival tablet makers will build fewer tablets than originally planned, according to a J.P. Morgan analyst.

In a research note released yesterday, analyst Mark Moskowitz said that non-Apple tablet makers have gotten an early "dose of reality" by failing to produce a high-volume tablet that comes close to matching the demand for the iPad.

As a result of the "weak showing" of products such as Motorola's Xoom, Research In Motion's PlayBook, and Samsung's Galaxy Tab, many tablet makers have cut back on their plans to build tablets by around 10 percent this year.

As a result, Moskowitz estimates the number of tablets that companies collectively plan to build for the year has dropped to 73 million from the 81 million he forecast in March. Among global tablet makers, only Apple, HTC, and Lenovo have kept their build plans intact since March. Other companies, such as Acer, Dell, Motorola, RIM, Toshiba, and Samsung have cut their build plans by double digit percentages.

"We do not think the first generation of tablet offerings from the non-Apple tablet hopefuls stand to offer compelling price and feature sets to drive incremental purchasers within vendors' projections," the analyst said.

By far the leader, Apple plans to build 38 million iPads this year, followed by Acer with plans to build 8 million and Samsung expecting to build 6.5 million.

Looking at the iPad, Moskowitz doesn't believe that shipments are being limited by timing or supply chain problems. The analyst still expects Apple to ship 6.75 million iPads for the quarter ending in June. For all of 2011, Moskowitz is forecasting iPad shipments of 29.6 million, giving Apple a 62 percent share of the tablet market for the year.

Despite the anticipated downturn in manufacturing non-Apple tablets, the iPad and its rivals still stand to affect the overall PC market, believes Moskowitz.

"On a relative basis, our assumptions of total tablet shipments in 2011 amount to only 3 percent and 11 percent of total handset and smartphone units, respectively. In contrast, our tablet unit assumptions amount to 32 percent and 21 percent of desktop and notebook PC units, respectively, which we think means that tablets stand to be big enough to have positive (or negative) spillover effects on the broader tech food chain."