This news is a deal breaker for me. I have more gamecube games than Wii games and will not buy a new system without backwards compatibility. My reasoning is simple: Counter Clutter. If I get a Wii U and I already have a Wii and the Wii U won't support everything that the Wii supports then I have an extra console on my shelf for less games. If, however, I can play everything on a Wii U that I can play on the Wii I can take the Wii off my shelf.
Besides: I really like using gamecube controllers with some Wii games. I would never even play many Wii games on a Wii U so it's not like it can even boast complete backwards compatibility.
If, however, some third party develop makes a Gamecube style controller and the Mod community emulates a Gamecube on the Wii U to use such a controller I think I would get a Wii U.
.......
This is probably why a Slimmed down Wii without Gamecube support is being released this winter. If that does well they can assume the Wii U will do well. If it doesn't they will probably work Gamecube support into the Wii U. That means we all have to boycott the slimmed down Wii to send a message to Nintendo.