How do you know this? It wasn't under warranty. I had it over a year before I sent it in. Once again if it breaks for unexpected reasons, you don't have to pay for it. Remember what happened with the first batch of 360's.
Yeah. They wouldnt service them for free, so everyone bought a 2nd one. And then 3 months before the PS3 launch, Microsoft changed their service agreement, and everyone shipped off the brokeass 360's. (I know 2 people that did that)
EDIT: Yeah, they now have 2 360's.
Also, you really lucked out on getting your DS replaced.
Once again if it breaks for unexpected reasons, you don't have to pay for it.
While it is under warranty. Once the warranty is over. They don't have to do anything. ;)