The anatomy of a 'bow'.

[Sparky]

So then why do we lap our CPU's, Heatsinks, waterblocks? So even when I lap my CPU on a piece of thick solid glass (very flat surface) down to 1200grit, my CPU still isn't flat?

It is never going to be perfectly flat. But the fact is, after you've lapped your CPU, it is much flatter than it used to be.