I have noticed that happening alot lately too!!! Actually it happened to me not like 2 weeks ago. I read that book "he's just not that into you" recently and the guy in that book said it's just a cop out. he said guys do that to create the illusion of leaving it up to the girl and putting no pressure on her, but he goes on to say if a guy really wants to take a girl out he will get her number. so that way he is in control. as a guy he said you can give the girl your number also, just for insurance, but for a rule of thumb the book says never to date a guy who doesn't atleast make the effort to get yours. I don't know how true that is...... but i find it very interesting!