Mainly we don't need new ones because the 3 year old one is still doing the job. That wasn't the case a decade ago - your 3 year old PC was seriously out of dat

Mainly we don't need new ones because the 3 year old one is still doing the job. That wasn't the case a decade ago - your 3 year old PC was seriously out of date and couldn't run most games released that year and probably not install the latest OS release. This rapid progress has flattened out considerably. Now people upgrade to get nice features such as retina displays or SSD drives, but that's optional (so you don't do it if you don't have spare money laying around) and the benefit is much smaller than going from a 90 MHz Pentium to a 450 MHz Pentium III.