You know, that's so common with iMacs in general. The G5 and Core models have issues with BGA chips separating.

It's easy to point the finger at the design but I think the wrong portion of the design is blamed. The part that is poorly thought out is that it's impossible for "normal" people to clean inside. These things get _very_ nasty inside because people can't easily open them up and dust them out. More dust = more heat = hot chips = BGA death.