That seems to be the case everywhere. In Cisco, I know that one of the JP's predecessors, Sri S. came from Microsoft and brought a number of people from MS: managers and there was even an engineer who was soon given architect role. The worst was when at one of the meetings they were praising their culture in Microsoft - they still didn't feel like a part of Cisco.
That's what happens with people in every situation. As an example, immigrants from same country tend to meet and form a group in foreign country. When it happens, they don't integrate, and usually they highlight all the bad sides of host culture as compared to their own.
In the same way, these groups from other companies, when they are together, seem to belittle their employer and culture that was created before they joined company.