Thoughts on adding bullet proof glass as a customization option?

I finally added armor to one of my cars last night. One of my crew members said that at 100% armor, it takes more than a single grenade or rocket to destroy your car. I haven't seen this actually work or not work, so I'm not claiming that it's a valid statement. If it is, though, I think that it's kind of silly that bullet proof windows/windshields aren't an option.

So I can possibly survive a direct hit from a rocket/grenade in my armored car, but someone with a pistol can kill me through the windows? Seems a little odd...

Thoughts?