The card passing isn't just a fun thing. There are a few cards in dominion that link decks, such as masquerade, jesters, possession, and they tend to be quite complicated since changes to each deck are not made in isolation. The impact of masquerade does unfortunately depend upon the kingdom, deck contents, hand contents, the number of players, etc.
The card passing will typically equalize the worst card in each opponents' deck (or more specifically hand). If you deck is better than your right hand opponent's you can mitigate this equalization by trashing the passed card (and many players just ignore the implications). However your opponents cannot immediately mitigate a bad exchange, and that bad exchange could be due to skilful play, luck, or general deck quality.
This leads to the situation where an action "draw 2 cards, you may trash a card" appears worse than a masquerade. The lucky turns 3 and 4 where you can exchange an estate for a copper are not balanced out by the unlucky turns where you exchange a copper for an estate, since the masquerade trashes the estate. The partial mitigation of this bad result, regardless of future turns, goes some way to explaining Geronimoo's simulation.
Don't think about masquerades and iggs too much.