I don't think it's so much planned obsolescence as the perception of such by society.
My car is a 1994 Intrepid. All the buddies are" Dave, get a new car"
Why? It serves me well, does what I need and is dependable..Ok, so I lost a brake line Monday and had to drive like a formula 1 driver for 60 yards to save my life!
My point is that we don't need to toss things away when they are still serviceable but we choose to from either public pressure or from just having it programmed into us.
A well tuned P3-1000 w/512mb ram will do most anything you need for day to day use on a PC
A AMD X2-3800 is still an excellent machine.
We replace by choice, not by need..Excepting the gamers of course and in that case nothing that exists is fast enough for them!