Can someone explain the difference between this 2 positions

with the queen on d6 black is doing just fine

what i maybe understand is the queen on d6 prevent white developing the bishop to f4, but anything else?

I believe it's a matter of tempi.

In the second diagram black takes the pawn on d5 and then moves his queen to d6. Thus spending to moves to place his queen on a square it could have reached on a single move (black loses on one tempo). This queen moves have meant that for the longest time most of the chess intelligentsia has deemed this defence as "second rate".

But in the first diagram black has burnt to whole tempi to move the queen away from the d8 square and back, which means that black gave white a free move. Scandinavian practitioners have often talked about solidity as a counter argument but praxis has shown that Qd6 is a far superior aproach. 

The positions clearly show this extra tempo loss when compared.

On d6 the queen not only controls f4 but also facilitates rook connection but since I barely bother with the Scandinavian defence other virtues of this move are lost to me.

Thanks for the explanation. I just look at it as i want a defense against 1.e4 with the fianchetto bishop, i also use modern/pirc as well

Don't think there is much difference in the positions, would prefer white in either case. As is often the case when trying to use statistics you are finding subtlety that doesn't exist in reality.  So GM's find Qd8 more solid because out of they way, and can't be attacked by Nb5etc.