I've long argued for this change. Thirty seconds simply isn't long enough to decide if you like a relatively unfamiliar song (or a familiar one in a new arrangement) well enough to pay for it. I predict that this will indeed lead to more music purchases via the iTunes Store, which is Apple's argument to music labels in support of the change.
I can think of at least a couple of occasions where I've taken a chance on a song based on its short clip, and found that the clip is the equivalent of the 30 seconds of really funny material in a trailer of an overall lame ninety minute movie.
The report says that Apple got push-back on this change from some recording labels, presumably for fear that people would either just listen to the track samples rather than buying the whole songs or somehow record them. That's a ludicrous argument, but I'd be perfectly content if Apple appeased them by providing a lower-quality sample to make such unlikely piracy even less realistic. After all, when I listen to a sample on iTunes, I'm not trying to assess the sonic accuracy and every nuance of the song; I just want to understand what I'm buying before I buy it.
Thank you, Apple, for making a rational business decision that benefits the customer.