It's a shame that MS couldn't have put clear instructions about how to prolong the life of your machine, but that would be admitting they know there's a problem, and I guess we have the right to expect something like that to just work and stay working if we plug it in and leave it on.
I imagine that if the advice about restricting yourself to a few hours at a time, making sure it's well ventilated, and not pressed into a 3 inch carpet, and other such things, had got thru to everyone there'd have been less returns.
At the same time, it should be capable of being left on for weeks, same as a PC.