The Beatles on iTunes isn't exactly big news; it's not as if their catalog has been unavailable or under-exposed.
What would be big news is if they let iTunes put up as much as possible from among the unreleased recordings by the group (including but not limited to the vast array of bootlegs that are out there). This could include content from the original reel-to-reel Abbey Road studios tapes, all available demos and rehearsals from the era, etc.
99 cents per track, no promotional or printing costs for Apple Records, no need to worry about hitting the top of the charts with a particular release, etcetera. And there would quickly be a huge volunteer industry of people listing proposed albums to self-assemble.
Even just with pirate CDs and downloads, the amount that's currently available greatly exceeds their official canon, and indeed is so vast that the hard part is figuring out what bits are of particular interest, as they frequently in the studio already knew what they were doing before the first take of a given track.