@BlazeHedgehog: I have heard it was 1 free patch, after that it is like 40k; and I am pretty sure Bungie's sweet talk was "hey we are making Halo 3".
This is mentioned on the Penny-Arcade Report article on this same subject. It read as if to say that the second "patch" also included paid dlc content. So it made business sense for Microsoft to allow it so that they could also make some more dough off any dlc that got sold. At least, that's what the article read like =)