You do realize that airplanes are made from aluminum, right? Are you seeing airplanes falling out of the sky everyday because 'all aluminum eventually fails'?

People love to snow you with their technobabble about how aluminum can only handle so many stress cycles, etc. This is all nice theory, but I think you will find, in practice, only a very small number of aluminum (or steel, or carbon) frames break. Just do a google search on 'broken aluminum bicycle frames' - you'll find very few actual reports of broken frames. This is the difference between theory and practice (and common sense).

Here is a question which none of the 'all aluminum eventually fails' crowd never addresses: 'what percentage of all aluminum bikes in existence have failed due to repeated stress?' - I don't know what that number is, but it has to be very small otherwise bike companies would have one heck of a lot of lawsuits to deal with.