Don't dismiss it so lightly. I think a MacRumors app would be quite useful. Reading from the browser involves a lot of unnecessary re-rendering (and usually re-downloading) of lists. And it isn't optimized for the iPad (or iPhone) screen. Of course, the latter could be done by MacRumors themselves with an alternate CSS.
What would be more useful would be a generic vBulletin-reading app. vBulletin is probably the most popular forum software out there. does vBulletin have some sort of API, so that it wouldn't be necessary to "scrape" content? I assume presentation is largely or completely determined by a CSS "skin", so maybe an API wouldn't be necessary. Still, there may be enough configurable options that it would be difficult to reconcile the differences between various sites.