> Are other encyclopedias or sources of information less or more likely to fall prey to this kind of bias?

I think it's less likely, because other encyclopedias are written by paid professionals (or at least some cohesive group whose reliability you can evaluate).

> Maybe in Wikipedia it's just more open, so you notice it more?

I think it's more likely on Wikipedia, because no one there is getting paid, so you have to ask yourself, what's their motivation for doing so much work? Sure you have the altruistic gnomes, just laboring to do a good, fair job for its own sake. But you also have people with an axe to grind, propagandists, and other obsessives, and they contribute to basically propagandize their POV. The dumbest ones get banned, but the smarter ones learn to twist the rules and use things like slow long-term persistence to get their way.