I've tried YC on the iPhone through Safari as well.. it works well enough.
However... IPB is a dedicated app put out by the software company that built our forum. Not only is it faster than Safari, but it enables Push notifications for a whole list of functions ( messages, following certain threads, when users reply to one of your threads, etc) Much better user experience than through safari for the iphone. I would like the site administrator to look into seeing if this is a free option he can enable for YC.