I was afraid of this. I had read a rumor somewhere that certain characters wouldn't be showing up Prisoner of Azkaban. I had hoped that one particular rumor was just that, because Quidditch is such an intregal part of the book, especially the final pep talk. How could you deny him that small moment? Alas,
Sean Biggerstaff has posted on his own website, saying in effect, his Quidditch days are over, breaking hearts everywhere. This really bites, because there were so many moments in PoA for Oliver to shine like hearing about the Firebolt. They'll probably shift his lines to someone else, like the twins. Oh well, I hope they manage to get the rest of the damn movie right!