Apple has finally rolled out the 90-second samples on songs that are longer than 2.5 minutes, sold in the United States, and that iTunes has managed to equip with the longer preview.

Apple CEO Steve Jobs offers iTunes users more time this holiday season to sample a song before buying.

Some bloggers and iTunes users have questioned why longer previews don't accompany every song. As first reported in August by CNET, Apple approached the top-four recording companies last summer about the longer samples that iTunes users can hear to test drive songs before buying. Researchers say that longer song samples stimulate sales.

According to several music industry sources, Apple has only acquired licenses to the longer samples for the United States, but the company is in talks to acquire rights to extended previews for overseas markets. As for U.S. iTunes users who find a song that otherwise should be eligible for a sample but is without it, the sources said that Apple is hard at work attaching them. It takes time to make the switch but it should be completed very soon, the sources said.

Apple came close to announcing the extended samples last fall. Apple secured the okay from the labels and was ready to announce the previews at a media event on September 1. The event came and went without a peep from CEO Steve Jobs about the longer samples. Turns out that the National Music Publishers Association (NMPA) read CNET's story about Apple's plans and informed the company that as far as they were concerned, Apple also needed their approval or there was going to be a problem, managers from the NMPA told CNET.

They told Apple that the trade group, which represents song writers and music publishers, wouldn't necessarily have a problem offering the songs "gratis," or for free, but they wanted time to study the deal, which they said Apple didn't offer them.

Since then, Apple wrote independent record labels and told them that the company planned to offer 90-second previews on songs longer than 2.5 minutes. Apple said that the only way for the indie labels to opt out was to remove their songs.

That the Music publishers were able to hold up the offering illustrates growing their growing influence in the music industry. This is one area of the business that typically is still profitable. In the past, a label's recorded-music division largely steered the ship. But recently, labels have turned to music publishing for guidance. EMI Group tapped Roger Faxon, the former head of the label's publishing arm, to run the entire company.

If music publishing's power continues to grow, look for David Israelite, the NMPA's CEO, to step more into the spotlight.