The rich text situation is somewhat different on the iPhone than it is on OSX/Cocoa. There is no NSTextView, for instance. The only "easy" rich text solution on iPhoneOS is a UIWebView - which isn't exactly cheap in terms of CPU utilization. Ironically, a visual effect such as a page curl is likely far cheaper due to the GPU support than reflowing a bunch of rich text.
My comment was referring to NSTextView which is present in OSX/Cocoa. NSTextView is extremely powerful and feature-rich. UITextView is.... not so much, of course. :)