All RNG's based on pure software (i.e. not taking external data from atmospheric noise or things like that) are pseudo-random, because the computer is a deterministic machine and doesn't have a source of true randomness. But the thing you say about crits shouldn't happen with any half-decent RNG implementation. While it's true that in a pseudo-random generator each number depends on the previous one(s), this dependence is implemented with a chaotic function which is highly unpredictable. It can generate streaks of "good/bad rolls" like true random numbers.
Maybe in that game you mention the programmers purposefully coded some logic on top of the generator to guarantee that you get X% crits over a period of time, or something like that. This is what is done in slot machines. They have a minimum and a maximum of money that they will give for every X coins that go in, and there are people who exploit that. But this is additional logic coded on top of the generator. I've always wanted to see the core code for a slot machine.
By the way, I have been playing ADOM for years, have a bunch of wins under my belt, and I don't think I have seen more than like 6-7 surges of power in my whole ADOM career. Incredible how some people get so many of them!