Do windshields get weaker over time?

Recently, I was pissed off and decided to pound the bug on my windshield that was really makin' me mad as I was working on my car... BIG mistake. Now there's a nice crack in it that runs in 3 or 4 directions. I plan on getting it replaced very promptly... But I was wondering. The windshield in the car, until now, was flawless with the exception of a minor chip (The chip was not near the location of the crack) and it was about 12 years old. Now, I know I was mad, but I'm not the kind of guy who squishes a bug as hard as he can to make him feel better about himself. In other words, it was a pretty light pound. I definitely wasn't expecting any after effects... So, what do you think? Do windshields indeed get weaker over time?