Agreed. A good wireless controller and connection to the TV (wireless preferred) could help pull this off.
GameStop gets to define the controller that will be used and to strongly encourage developers to support that controller. One of the big wins for consoles is a known hardware and control setup. Right now no tablet comes with or can expect a handheld controller. A GameStop branded tablet could do that.
Also, GameStop could sell games for their tablet only through their own online store. Then they could sell the tablet at a loss and make it up on the games - just like the console makers. What would be hard, though, is forcing developers to ONLY sell their games through GameStop. But Steam does pretty well, I guess.
Toss in some good parental controls (I want this account to only see Y7 games) and that would give parents a warm fuzzy about the system. (But kids would hate it, so maybe that's a bad idea. But the kids will likely figure out a way around the controls, and many parents won't bother to set them up.)
To me, the trick is NOT to just release a GameStop tablet and a controller. But to release an entire gaming environment. Playstation Network and XBox Live have led the way, but they had years of experience and huge piles of money behind them.
Tablet hardware has certainly reached the point of being powerful enough to be a viable gaming platform. A tablet with a few tweaks to make it extra gaming friendly could be a winner.