This is true. When you're a freshman you don't know anyone yet, but no one else knows anybody else either. So people are much more compelled to make friends. After a couple years your circle of friends kind of crystallizes, and those whom you don't know aren't that eager to stretch out of their little circles either.

I went through the "moving to a new place" experience a few months ago when I moved to Germany for 3 months. It was really odd, as it was the first time in my life when I really had to objectively think about how to make new friends.

And the best advice I can give about that is: DON'T go live on your own. At least not for the first few months. Go live with other people, particularly with people who value having a good vibe in the house, and not just living together to share expenses but never looking each other in the face (if you're going to Germany, look for "kein zweck WG" ;). You'll end up becoming friends with them, and meeting their friends that come over from time to time.