Something I've been wondering about myself... Can't answer your question, but can only point out that you are a bit mistaken to treat Europe and ex-Soviet territories (especially their European part) as two completely separate worlds, since before the Iron Curtain came to exist, they shared quite a bit of common history.
I know that answer is not in this forum. However I expect someone may be heard of a good book to explain this. A book based on research an anthropological study but not on sentimental history of the problem. (By the way somebody down voted my question. Isn't this a legitimate question?)
I almost downvoted you because you said "Or Jewish people are just more outspoken?" which sounds a bit like "Or are they asking for it?" but I decided it was probably just a communication problem.
There are lots of books on this topic. "Why the Jews" is supposed to be good. There's also "Antisemitism Explained" by Dr. Steven Baum, my former psychiatrist, which I would expect to take a deep psychological analysis (but I haven't read it).
More reading about anti-Semitism in that territory: http://en.wikipedia.org/wiki/Khmelnytsky_Uprising#Jews