Apple have always been against the remapping of hard buttons on iOS devices and I'm not surprised they didn't go for an orientation-based functionality with the iPad.

Remember that camera apps were not being accepted for the app store when they used a volume button for shutter release. Now Apple has added that functionality themselves so third parties can too. Nevermind the volume button sucks as a shutter release and having the lens on the bottom right of the "camera" is equally terrible.

So it won't surprise me if Apple at some point added an option for something like this on the iPad. I don't know if I'd ever use it myself, so I'm just saying it wouldn't surprise me.