Per
THIS article on Forbes (they were actually quoting
this blog entry), the sprue actually does affect randomness.
However, they say that for normal tabletop gaming, it doesn't make that much of a difference. Here is the relevant portion of the result blog entry, copied and pasted for your reading convenience:
"It’s worth stressing that based on our tests you would need a lot of dice rolls before you saw a meaningful difference in any of these gaming dice — roll a thousand times and maybe you’ll see 5 or 10 less of a given number than you’d expect (or more). So for gaming purposes both dice will work just fine. Seriously."
"But that said Chessex dice (and in theory any rounded-edged dice) are going to roll less close to true. Because of the randomness of the process that changes the shape of the dice, there’s no way to predict which faces are going to roll better or worse. Indeed this means that you could have dice that are “lucky” and roll high more often or crit more often, and “cursed” dice that seldom roll 20s and fumble more often."
"With GameScience dice, on the other hand, you know that the 14 will roll substantially less than any other result — so technically the dice will roll low, but the 20 should roll just about as often as the one, or the 10. If you carefully sand the flashing down on the GameScience dice you should get a result that is very close to being truly random."