The same thing happened to me, on my iPhone 3G.
Except I dropped it, drunk, and split the casing open around the mute switch. I played dumb ( "look, the casings coming apart here...I think that's why the switch doesn't work" ) and because it didn't have water damage, they replaced it.
I've thought about doing that with my current iPhone4. It has a couple of scratches -- nothing major -- but there's one scratch/quasi-crack around the home button that seems to have taken some of the sensitivity away from the home button (i.e. you now how to push it with purpose, and double-taps are more difficult). That one isn't my fault. If it gets worse, I'll take it in, hopefully for a replacement.
So, I guess my point is: I agree.