Mostly because I'm a WEAK minded consumer and money burns a hole in my pocket just like MOST of you on the Anandtech board If I didn't buy parts here and there...I'd never save enough to build a new PC.
I only buy components which are REALLY good and at REALLY cheap prices which are NOT offered frequently at low prices (i.e., get them when they're cheap, or pay top dollar because I HAVE to get them to complete the build). I don't buy the really dynamic components early (e.g., mobos, CPUs, video cards) because they constantly improve and the prices drop rapidly.
From March through today, I've got the case, PS, 2 HDs, DVD-Rom, DVD-RW, Sound Card, fan controller, and TV Tuner/video capture card all of which are prices HIGHER than I paid (or at lease within a dollar to 2).
My RAM should have arrived today, the video card/mobo should arrive next Wed. and I'll order the CPU/HSF after September 25 AND as soon as a good deal comes along.
I buy the "high end" parts just before I'm really ready to build the PC (which also happen to be the parts which improve and/or drop the MOST in price over time).
My system works for me.
Bud