It's strange, because my experience is completely counter to that. I'm 30 years old. I live in a relatively dense urban neighborhood in Denver. I have many close friends that I see on at least a weekly basis and often much more often than that. My experience is very similar to the one studied in a great book:

Urban Tribes - http://www.amazon.com/dp/1582342644

Maybe it's a generational thing? While the political and social structures have definitely changed (particularly with regards to church), the end result is very much the same. I think the 'Generation Y' (god I hate that term) is showing a very different attitude towards community than our parents did. They're (we're?) settling into more urban neighborhoods. They value their friendships and relationships more than the previous generation did. They're relying on those friendships much longer and postponing starting families.

It really does seem to me that this generation is living gasp a much more European lifestyle than generations past. Having lived in Europe myself for several years, I can definitely see the similarities.