The way Steve vigorously came out against 7" tablets makes me suspect they'll launch one, too. His logic was rather questionable (you need to sand your finger tips to points to use apps on a 7" tablet, but not a 3.5" phone?).
What he probably means by that is that he doesn’t want any further fragmentation. A 7" tablet would need an optimized UI for the reduced screen size (you can’t just shrink down iPad apps or blow up iPhone apps), Apple doesn’t want that.
There won’t be a 7" tablet anytime soon (within the next twelve months) and that whole September business is based on pure speculation, not any sources or evidence.
And iPad 3 will be March 2012. It is too soon. iPad 2 might not even complete its worldwide launch by fall. The Fall rumour most likely is a 6 inch iPod touch launching in September iPod event.