Casino dice are the truest rolling dice you are going to see at a game table. I highly recommend them.
The dice with the pips out roll low numbers more often than high numbers. This isn't superstition, this is science fact. When you dig the pips out, the mass of each facing changes slightly. The more pips, the less mass that facing has. And because of momentum:
P = m * v
the more mass a side has, the more momentum that side has. This makes it more likely to rebound away from the table. If the die has rounded edges, then it requires less energy to roll over or bounce to another face.
Factoring all this in, the "6" face has more mass taken from it, therefore it has less momentum => less likely to roll over => more likely to stop with the "1" face up. The same can be said of the "2" and "3" face, but these become less pronounced as the difference in momentum of each face pair becomes smaller and smaller.
Of course, if you are using faces with numbers instead of pips, one has to calculate the mass removed from each face at that point. That is a lot more calculation, and not terribly useful, as the difference in momentum is likely to be very small. Since pips are the most popular D6 style, however, it is something to consider.