yeah but i do that too through my airport express to my strereo. its nothing new or special.Streaming from my Mac to the TV is the reason I'm looking at it.
I can stream my music to it from my MBP, sat on sofa..
Stream a movie to it.
Also, the Apple TV just connects to your lappy.. so you get "front row" on the TV.. you could leave the Mac upstairs just on.. or, sync your favourites albums to the Apple TV and play them - think of it as a static iPod with movie support
Express is very good.. and certainly to be used aswell as an Apple TV not instead of!