Why is white winning?

After 1...Kg6 2.Qxd3+,f5 3.Rxc3,Rxc3 4.Qxc3 white has candidate passed pawns on b4 and e3.  Exchanging down into a pure queen ending seems to be in white's favor. 

After 2.Qxc8?,Nxc1 white just has a draw as the queen liquidates white's queenside by force: 3.Qxc3,Qa6+ 4.b5,Qxa4 5.Qxc1,Qxb5+

Well after the forced 1..Kg6 2.Qxd3+ white is a pawn up with check against the weak king. The rook remains loose so 2..f5 is forced (anything else Qd7+ again and the loose rook is dead).

After 2..f5 3. Rxc3?! is not needed here as that pawn will fall anyway. Much stronger is 3.g4!, forcing a defensive move and white will be 2 pawns up as black has no time to take the b pawn.

In some queen vs queen endings 2 pawns up may not be enough due to loose pawns and prepetual possiblilities, but not here as white's pawn structure is solid and white's queen remain in the center of the board for both offense and defense.