It's not just Fox (X-Men 3, Ice Age 2, etc.), but Viva titles in general including Disney's (Cars) which have been showing significant delays.
We really don't know why but I can only speculate:
Probably their "yoyo" pricing has backfired on them. Alam na yata ng lahat na nagiging P299 ang titles nila, so maybe just a few really buy their titles at P750/P900. So this doesn't give them a reason to rush in their releases in time with the international release. Maybe they are still trying to figure out the best way to solve this and one possiblity is to price new titles at P550, just like their most recent ones (Little Mermaid Special Edition, High School Musical)...
Or they could be having problems with re-packaging lately. (Maybe the one in-charge with packaging has already been fired because of numerous misspelled words on their recent DVDs?
)