The culture of Twitter is different, though. It isn't just Facebook with every update cut off at 140 characters. Many have noted that on Twitter there's a widely held expectation that you'll at least try to be witty. (You can't spell "Twitter" without "wit".) I'm no sociologist, but if I had to guess, there are probably two core reasons for the different culture:

1. Pseudonyms (or first-names only) are allowed and widely used. So there's less expectation that your Twitter social life has to match your offline social life.

2. The asymmetric follow model. You can follow someone without them following you. You can unfollow someone and then change your mind and follow again without them even noticing.

Combined, the dynamic of Twitter is that you follow based on interest, whereas on Facebook you friend based on acquaintanceship. That produces a pressure to be interesting.

I'm not a particularly heavy user of either Twitter or Facebook, so please weigh in if anyone thinks I got this wrong. But this is why they feel different to me.