It's a coup for Apple, as Elton is a legendary musician, and a display of faith in iTunes by Elton himself. Now, as Infinite Loop points out, this is what many of us were hoping would happen with the Beatles' music now that their legal case with Apple had been settled, but it won't be the case.
Anyway, if you're a fan of Sir Elton and you're looking to complete your collection, fire up iTunes on March 26th.