Fractures in the glass is a possibility however I think Euf would have mentioned that if he dropped the glass before, he would have come to that conclusion I think. However the rapid temperature change is much more common, people do it accidentally all the time...I have to say it would be very uncommon to drop glass several times on a hard surface and have it not shatter...I'm not saying it's impossible...but still much much less likely to be the cause.It's the glass transition temperature...I'm not going to explain this concept, i don't have the years required look it up yourself if your really interested.

..."hard surface"...as in, nothing padded, tile, lenolium, wood floors...*shakes his head* I don't know what carpets you have in your house but if they are as hard as wood floors, you got ripped off