Hmmm, that's an interesting hyothesis, but I wouldn't think it quite explains why it does this while sitting for a long time? I would think that there's very little temp differential betweeen the inside and outside after it has been sitting for more than twelve hours, like it was last night when I went to go drive it. Night had fallen quite a while ago, so it couldn't have been some kind of greenhouse effect heating up the inside, then holding the heat until three hours after night-fall.

Anyway, you are correct that modern windows are much thinner. I heard this because that is one area where the manufacturers have attempted to save weight. This works quite well in fact, but the reverse side of that coin is that modern windsheilds crack and get holes from rocks much easier than old ones. I suppose the glass replacement companies don't complain about that particular trend...