There's a common misconception (I just saw it in a book by Bill Bryson, for crying out loud) that glass is a fluid, or a liquid. People claim that old windows will be thicker on the bottom, because the glass has flowed downward. They do not seem to realize that if glass hundreds of years old flows down, then glass over a thousand years old would have large gaps in it. This is not the case.
In fact, old glass has a thicker end because of the way glass was made in the past; glass wasn't quite flat, so there had to be a thicker end, and sometimes, that end was on the bottom.
So, please, stop repeating this one, people.