Why AC points on PCB are separated by a hole
Yes, it's for a sort of clearance. 

Depending on the voltage and the environment (eg. dust, humidity) for safety (and safety agency approvals) you may need clearance across surfaces that is in the 8mm or even greater range. That's inconvenient in a 2-dimensional design like a PCB (on a barrier strip or switch, you can have a 3D barrier between terminals that increases the clearance across the surface). 

The name for the linear clearance distance on the surface is "creepage" distance.