I think it's how people "treat" their hardware contributes to this.
I was the younger brother in my family and my older bro always told me not to mess up his SNES or Genesis Controllers when I was a kid. Overtime because of that, generally don't "Go HAM" on controllers. Doesn't matter if it was a handheld like the PSP or DSLite, or a console controller like the PS families or Nintendo controllers, I've never had a controller "die" on me.
However my very same older brother goes through controllers alot, he's on his 4th 360 controller and managed to wear out my PS3's DS3 controller as well. I'll admit that other factors come into play like he mostly plays Shooters while I'm more of a JRPG's and Racer type of gamer however, we both play action intensive games like Ninja Gaiden.
But from my experience with controllers, the more mechanisms they add to these controllers (i.e. moving parts) the more that can go wrong. But as someone who never needed to replace his controllers and only bought more so that other people can play, I think alot of it has to do with "how" people are gaming on their hardware.
Now I've replaced parts before (i.e. for a fightstic)k, but anyone who plays fighting games knows that buttons will eventually go out.