Taking a quick perusal of the forum, I'd say your point is valid. Let me add this, if there's not a lot of discussion of iPhone apps, how would a sub-forum aide help that? That is if people are not discussing apps now, how would moving it to a new sub-forum correct that issue?
The first page of that forum has threads from 05/22 to today (6 days worth) Out of that time frame the majority of threads is developers promoting their apps. People by and large do not seem to be going there to talk about given apps.[