Maybe I'm biased, but I don't think this is going to be a terribly big thing. As a lifelong Beatles fan, I already own the entire catalog (on vinyl, then the '87 CD's and now the 2010 remasters). This is probably true for a lot of people. Then there are the folks who borrowed and ripped Beatles CD's to populate their iTunes folders, or downloaded songs from unauthorized sites. The potential universe of buyers from the iTunes store seems relatively small to me. But then again, Apple (and Apple Corps) have a pretty good track record.