its not that people specificly go out to buy older computers. the fact is the average HOME users doesn't upgrade/replace their computer for at least 3-5 years. Im not talking about 20 year old jimmy the guy that 'needs' the best and newiest in hardware every month. More along the lines of mom and dad or aunt Phillis or little cousin Jane whome are realy the wider home market PC owners today.
They don't upgrade because
1. they don't know what it means or that it can be done
2. they see no reason to because the computer they got now works fine
3. cost is too much just for a an extra do dad they don't see needing
they are also the typical user that you know. don't know how to to defrag a hard drive or even empty the recyle bin. has to get the kid from down the street to install a program for them.
May be funny sounding but that is your wider base home PC market.
My advisor ( when I was in collage for Comp Sci) said statisticly the average home owners computer is 3-5 years behind in hardware technology. When you program you program with the hardware capabilityes of the target user in mind. Obvious a lesson many of software houses never learned.