The addition of The Beatles to the iTunes Store roster has been predicted for years. Back in August 2007, this writer noted "Some pundits have suggested that the invitation's tag line "The beat goes on" is a reference to The Beatles, but how often have we heard that rumour?"
As noted in that article, if Apple Corps doesn't get a move on, early recordings by The Beatles will be out of copyright in the UK before they are available for purchase as digital downloads.
Speculation is also circulating that Apple will make other announcements, including the long-hypothesised music subscription service, and the ability to stream music (and possibly other types of content) owned by users to whichever device they happen to be using at the time. The release of iOS 4.2 has also been expected for some days.