I think your statement is only accurate in gaming.
As it stands, any computer now above 1ghz with around 512MB of RAM and 40GB hard disk space will run fine. Video cards get outdated quickly if youre into big games, sound cares are pretty stagnant.
Like if youre just surfing the net, using Office apps, listening to mp3s, maybe playing some lower end games (non FPS), I think computers built in the past year or so have been effective for a long time and dont look like theyre going to stop.
If you get a 1.5ghz P4, 512 RAM, 40+ GB HD, SB Live!, and a good LCD monitor, you'll be in business for quite a while before your hardware gets old on ya. Unless you want to play Doom3 at max res online that is.
Software has fallen WAY behind hardware recently, and there is a surplus of hardware capacity now that should let computers last longer, at least until the next release of Windows in 2005.