I'm not 100% sure on this, but it "might" have something to do with the way the hinges and the lift supports attach to the glass. I remember reading somewhere that GM discovered a problem with the way it was designed, the rubber was coming detached from the glass. When the rubber started coming off the glass, it would cause stress on the hinge points, and where the lift supports attach to the window. In 2005 they redesigned the rear window glass to a new "frameless" design. Instead of the hinges, the latch, and lift supports attached by the glued rubber frame, they are now actually bolted through the glass with the new design. If you notice on some 2005 and 2006 models, the rear glass will have a black plastic "shroud" across the top of the glass, this is a cover to hide the hinges that are bolted through the glass. Whether or not this has anything to do with the cause of your window exploding is anyone's guess, but I just thought I'd mention it as it's a possibility.
I also remember in the 90's my dad had a Chevy Blazer and he had the same issue. For some reason he went through 3 windows in a little over a year. I remember the first two times the glass was broken when we returned to the parked truck. But then the third time, the window "exploded" when my Dad tried to close it. I was standing right next to it, and I saw it clearly. He put his hand of the glass and went to push it down to close it and it just exploded. We initially thought that he slammed it or something, but we saw that it had not even latched shut before it broke. The dealership and the glass shop both said that the lift supports had too much "pressure" and that's what caused it to break.