If people are seriously worried about it, it's not that hard to run a chi squared test on the dice to make sure they're reasonably fair. Of course, no die is "perfectly" random, but most are close enough for gaming purposes.
The chi squared test isn't hard to do, just a pain to record the required rolls. The math's pretty simple.
Edit: Link added for the interested (although I have no affiliation with the linkee)
http://deltasdnd.blogspot.com/2009/02/testing-balanced-die.html
Vale,
JohnS