Keith,
A little more thought might then bring you to consider what it is about BGS students (note that I use the term BGS students and not BGS) that makes them more disposed to make posts, than those of all of the other schools put together. I do not claim to have the definitive answer to this question. All I am suggesting is that the question exists and readers should consider it.
I think we all do consider it. The reasons I think that BGS students post their happiness is simply that BGS as a whole is very p-proon aware, with a terminal set-up that students log onto during breaks. Not to mention that there are a fair number of students. The whole setup exudes high sprits and good nature with many people keeping in contact with each other and knowing each other's p-proon handles. I think it a genuine comment to say that everything about the BGS experience is positive.
This is not meant to say that other schools are not the same, but that is my reasoning. If you want the definitive answer I suggest the other schools start looking inward.