My Singaporean roommate complains about this very thing. He thinks it's a politeness thing, as in, Americans will say "Let's do this again sometime," to sound polite, even when they have no intention of doing so.
I know that I totally intend on following up, but starting up new friendships often seems like a lot of work. Most of my friendships come from work, friends of friends, or other regulars at the bar my friends and I all go to. It seems like less of a risk after you randomly socialize with them a few times.
