True, that is probably the reason why 2" is the hole size. It has been a while since I have bypassed a fence and it would be negligent to have something that worked as good as a ladder!
Normally you find an area that can be lifted up and you can expect barbed wire at the top, climbing is out the question though.
I would go for the bigger holes if it was my fence just so people don't vandalise it by lifting it or cutting the wire.
Of course, dense vegetation would be even better, as you say.