It's all about UI experience. Have a look at iWork for iPad. There are some very nice tricks/effects you could add in an app and make them much more user friendly than browsing the normal website and zooming in/out constantly.
I think the iPad screensize is large enough without needing to zoom in and out? In any case it always nice to have some tool that help users navigate the forums on future iPad. Bring it on!
think an iPad app would be awesome and would achieve good sales. personally I wont be getting one as I'm MacBook Pro and iPhone equipped