Computers, if taken care of, will easily last a decade or more. Doesn't matter if it's a Mac or a PC.
The problem is, at that age, they are very limited compared to modern machines. This will come as a shock to some Apple acolytes, but a ten year old Mac is NOT going to run the most modern software well. Steve Jobs was not a God, despite what you may have heard, and his machines are subject to the same problems of obsolescence as PCs.
If you run an old machine (Mac or PC), and it does what you need it to do, fine. Keep using it. No reason to upgrade or replace a machine that is doing what you need it to do. I have computers all over my house (currently 9 of them), and they run the gamut from modern, high end gaming machines to a 10 year old clunker that I use just for basic internet surfing in my kitchen. They all have their place.
