Right, think of it this way
Gamecube - $150
Mem card - ?
Game - $29.99 or more
Using your gift voucher, whether it be applied to the Cube itself, or for the game, saves you $50.
Hence, if you think of the voucher being used on the Cube by itself, then yes, the Cube is only $100
However the combo is still well over $200
Make sense now? Yes, the combo is over $200 but within that combo the Cube is still $150, so $50 off the combo could be worded as $50 off the Cube alone.
The way I see it, I'm going to buy a Cube, Mario, and the memory card and get a free copy of Starfox.
One of the clerks I spoke with the other day said they will be getting Gamecube bundles with Starfox in sometime THIS WEEK, so maybe you can try to get them to give you the voucher with the purchase of the bundle and save $10 or so on the game you buy (if you purchase two games)
Wow, long winded post...heh