Why is that? I think you're misled by OSX's numbering system, which uses .x where other operating systems might use whole numbers. In fact, I misestimated myself...I thought each dot-version represented a year, with Tiger being 4 years old.

http://en.wikipedia.org/wiki/Mac_OS_X_Tiger

However, Tiger is actually 8 years old. I don't think obsolesence in eight years is too horrible.