This. The difference between a Pentium and a Pentium II used to be so staggering that most people would upgrade.
Now, the difference in usability between a Core2Quad (2007) and a Ivy Bridge i5 (2012) is rather minuscule to most home consumers. I know guys who are still using a Q6600 as their primary processor for gaming, and it runs Diablo III fine for them; they don't even overclock. Hell, the only reason I got rid of my ancient Socket 939 Athlon 64 X2 4200+ (from 2006) was primarily because my motherboard crapped the bed (capacitors) and Socket 939 boards in 2010 were too ridiculously overpriced to even justify buying.
The upgrade cycle went from every two years to every 5-7 years. I don't buy a completely new system as often as I used to... even when I do, I still reuse a ton of the parts from the previous one since I tend to add new parts as old ones fail.