Sure but I already charge my iPad about once a week and it's never flat - 13 hours for video playback if you watch one or two TV episodes a day goes a long way.
I guess they could add a smaller battery, but I don't think that would reduce the weight by much — it's pretty small.
What iPads really need is better software. Safari, for example, is vastly inferior to the Mac version. And don't even get me started with how window management works on an iPad. It's total garbage.
Maybe with better software, I'd use it for something more computationally demanding than watching TV.