A commenter to my post below wrote:

I'm curious why you decided to call students and why you continue to do it. I'm not saying it's a bad thing, but I've never heard of other professors doing it, so it does seem a little odd.

My first reaction: What a strange question. Why does anyone congratulate anyone else on some success? Because it makes the congratulated person feel good, and the good feelings are well earned. Because it's a mark of respect. Because the congratulated person is pleased and even grateful for the congratulations, and the congratulator ends up feeling pleased in turn.

At the same time, maybe I'm missing something, because indeed to my knowledge this is a pretty rare practice. Is there a downside that I'm not seeing? One commenter said, "I once congratulated a student on winning the award for second highest grade, and he said so, you thought someone did better than I did?'" Never happened to me, and I doubt it ever will; plus, even if someone reacted this way, it would hardly be a deep insult to me, or reflect deep unhappiness on his part, and it would tell me a little about the person's character (relevant when deciding on whether and how to write letters of recommendation for people). Another wrote, "I once got a letter (well, an e-mail) from a law professor saying that my final paper was really great, and 'deserved' an A+, but because he was 'not a nice person' or something like that, I was only getting an A. Thanks a lot, man. Thanks a lot." OK, I agree that this particular professor might want to decrease rather than increasing the personal touch.