Again I agree the Wii uses older tech so there is less need to cut corners on cheap parts during the production. On the other hand I still have heard of several Wii's needing to go in for cleaning (especially after SSBB came out as it was the first dual layered disc for the system). Nintendo stepped up immediately to take care of the problem immediately for free even for systems out of warranty.
The 360 has had a miserable failure rate. Every person I know of including myself who has had the system from before Halo 3 (practically everyone who jumped in during the first 2 years) has had their system RRoD once. But MS acknowledged the problem and has fixed all of those under warranty with very little hassle. And they seem to have fixed the issue on newer revisions.
I have heard of a few PS3's breaking with disc read errors and also from system updates but by no means has it been an epidemic (like the 360) as you may have implied. In fact I would even argue that the PS3 is more reliable then the Wii. I only personally know of one person that had to get theirs replaced (had the extended warranty from Best Buy). The biggest problem with the PS3 is that if it does break out of the warranty you are S.O.L. and will have to pay for the repair yourself as Sony doesn't do the customer friendly thing and take care of problems out of the "original warranty".
