I mean... how can you resist an extra game for 10 dollars?
The combat tanks game makes it worth it too.
That's actually part of most of the people I work withs selling strategy. O.~
I use the same strategy for the other systems too. 10 dollars for a game with the 50 dollar PS3 headset (SoCom) and the 12 months xbox live (with Project Gotham Racing, a headset, chatpad) for 20 dollars more than the year subscription.
Bundles are an easy seller when it comes to accessories. Sometimes it's impossible to sell otherwise though (I have seen places all over around here that have the Guitar Hero DS bundle still).