I'm not sure if this has been covered yet, but I doubt it considering the math-orientation of most people on this thread:
Whether there is a difference depends on your skill at throwing dice.
"But they're random!"
Auhm. Not entirely. HOW you throw dice Will affect their outcome. How you Hold them prior to the throw will affect the outcome.
If you know what you're doing, you can purposely skew the results. You can't get 6s Every single time, there Is still an element of randomness, but pointing it in the general direction you want is relatively easy.
Doing so with gobs of dice in your hands, however...
I've never seen anyone accomplish that. Not with more than 3 or 4 dice and most can't do it with more than 2 (they practice it for their Craps games).
This is because, as was stated about mechanics in the first response, when the dice are rebounding from each other it reduces the effects of your hand movements and how you hold the dice before throwing.
This is why Yahtzee uses a cup.