Why? Whats's wrong with sitting on the couch and browsing the web on a big screen?
Because to put it simply, browsing the web on your iPad looks and works so much better.
Plus you aren't taking over the tv with text that others read at different speeds than you. How fast are you going to scroll down the screen? Are you going to stop and wait for others? It's not like video where everyone's eyes are able to view and process at basically the same speed. There are all sorts of practical reasons why this doesn't work better than keeping the browsing to a personal device like an iPad. You might think that email, twitter, or facebook on your tv is a good idea but no one wants to see your twitter account on the tv screen while they're trying to watch tv.
The reality is the only thing that's worth putting up on the tv screen and better than any other device at that is
video and an iPad + Airplay is perfect for that. The solution is to have your iPad on the couch while browsing the web, searching for content, checking your facebook, twitter, etc. If you want some video to show on your big screen, just click a button. A keyboard style remote browsing and clicking to a tv screen 10 feet away will never beat that kind of ease of use, UI, and interaction.