No Gamecube version, huh? Only the 360 Live Arcade so far? If you want people to get Castle Crashers, I suggest making the game a little more readily available to the entire gaming audience.
As many people have already suggested, you should make the game available on the Wii's Virtual Console. You don't even have to use the Wii's controller, if you don't want to. They have a controller available to play classic downloadable games, so why not use that for Castle Crashers?
I honestly think you'll lose a lot of potential buyers for Castle Crashers if it's only available for the 360's Live Arcade. No one will pay $400+ for the 360 just for this game. Even then, there may not be many people who have the 360's online service that actually want to buy Castle Crashers.
I would seriously reconsider making it on the Live Arcade only. Even if it doesn't end up on the Gamecube, PS2, or Xbox, you should really make it for the Wii, as well as the 360.
Just remember this: it took Microsoft about 4 years to get 2 million unique users signed up for their online service. It took Nintendo about 4 months to get 1 million unique users. And with the Wii's free online service (along with the general excitement and anticipation of the Wii), more people will sign up for the online service. This only means more potential customers for you. I think a lot of the others on Newgrounds awating Castle Crashers would agree with me, but we'll let them decide.
Just take it into consideration, Tom.