A friend just got back from a computational linguistics conference in the U.S. She commented that she and her colleague had noticed that the best talks came from European labs, and that Europeans seemed more open to exchange of ideas than American researchers. This observation precisely matches my own experience and opinions.
In general, it seems to me that American researchers have little interest in any ideas but their own. All of their energy is spent churning out papers to further their careers. I think that this is due to the extreme competitiveness of the funding situation here. It results in thrashing - scientists spend all of their time maneuvering to get funding, based on safe incremental changes to their previously funded work. Anything not directly related to funding for their own research is of no use; it is as if they have blinders on. As a result, cronyism rules; established researchers will only help other researchers if there's something in it for them. If a new researcher independently generates original ideas, it is impossible to get ahead based solely on the quality of those ideas.
That's why the U.S. is losing its pre-eminence in science and Europe is gaining, as shown by an NSF study of where the leading papers in a variety of fields are being generated.