Apple had a deal worked out with Broadcast Music, Inc. (BMI), all four major record companies, and a contract with American Society of Composers, Authors and Publishers (ASCAP) that never limited preview lengths in the first place. Apparently that still wasn't enough to increase preview lengths, because CNET says the National Music Publishers Association objected and basically said, "No, you have to make a deal with us, too."
All of which just makes me wonder: how many different licensing associations does this
The music industry giants gave up a lot of their power (and money) to Apple in the mid-2000s, and it seems they've learned their lesson. Unfortunately for us users, this obstructionism means we end up losing out on neat features. As CNET notes, the current mini-battle over song previews is likely just a warmup for the headliner bout: Apple's predicted music streaming service.
Music industry execs already tried to get Apple to pay "performance fees" for its 30-second song samples; I can imagine Steve Jobs's response to that one was something like maniacal laughter followed by a hearty "No." If Apple does finally manage to get 90-second previews pushed through, it could be a good sign for its music streaming aspirations.