"Most PC users who complain about their systems being slow after 2-3 years are high-end gamers who wouldn't buy Macs because most of the games are not available on OSX in the first place.
For typical day-to-day office and media consumption use, even today's lower-end Windows PCs will last most people 5+ years."
And even the smart gamer would do a clean install of windows every year or two.