iMac is, by far, the Mac with most of the problems in the entire Apple's lineup.i think that the way that you use it is one of the factors in the reliabilty of a laptop.
if used as a portable then they're typically subject to rough handling that most desktops will never see.
damage that might be more likely to occur includes;
early hdd failure, case problems - cracking, hinges etc, screen damage... i'm sure there are more examples
And you're not going to move it around , I presume
Buy with your AmEx, they'll double the factory warranty.
Outside USA, AmEx is "crap"