You're only saying that because most programs are incapable of taking advantage of multiple cores, but if 8 core CPUs were the norm, I guarantee programs (where performance matters) would change.
If 4 cores are the norm now, and most programs cannot take advantage of them, what it the rationale for which things would change in the case of 8 cores ?
4 cores aren't quite the norm. The computer I'm currently at is a Dell XPS 13, the CPU is an i7-4510U, which is dual core. Regardless, in most circumstances, 4 cores are only just above break even point for parallel code, so the pay off isn't big enough.