Indeed, it's more about how much time you have per screenful than any actual region protection.
PAL games have more CPU time (raster lines) per frame to play with.
On the C-64 this is important because there is not a lot of time to begin with, so the more advanced PAL games just don't have enough time per frame to do their calculations on an NTSC machine. Also stuff is syncronized to the raster beam position, and so on.
Get a PAL Amiga and be happy, NTSC only software is rather non-existent.