Piston design is crucial since the piston forms the bottom of the combustion chamber, I have heard of B series engines in the states running 13.5+ static compression with well designed pistons on pump fuel.

dsp26 is correct, cam size also plays a big part, at the end of the day it's the dynamic compression which actually matters. It is possible for an engine with 13:1 static compression and an overly large cam to have the same dynamic compression as an engine with static compression of 10:1