I notice this too. Most people here login between 10am and 2pm. I think the main reason is they are tied to a computer at work. I am too, though web developing is what I do for a living. I will typically have 3 development servers going at once... one to write code on, another to refresh and see the results of the code and the last I will keep on the forum and refresh the browser once in a while. Typically, the connection speed for most of these folks is a lot faster then at home. Before I put in high speed at home, I would wait 'til I got to work if I ever wanted to find or buy something off the web. I think there are a lot of folks out there like that.
Kind of funny though, when I bring up the forum at 2 in the morning and there are a couple of users sitting on it. Must be for the night bite ;-)