The other night I played an IRL game. It was biased towards Dark Ages, but Goons was on the board (I think Marauder was as well). We both opened the same, and played largely the same except for one buy on $5 (I bought Cartographer and he bought Haggler). Halfway through the game I resigned because I was being slaughtered.
I proceeded to ask him how he got to where he did and why I didn't. He said he got lucky and I didn't. I said BS. Maybe there was some luck involved but there's no way I get unlucky on EVERY Goons board. He didn't budge. My conclusion: there's something he knows about Goons that I don't that he's just not telling me.
I fully acknowledge that Dominion is a high-skill/high-variance game. Put any scrub against WanderingWinder and he can win with a sub-par strategy (look over CR for my one game against WW for a perfect example). HOWEVER, the attitude I choose to take is that if I lost, I could have played better, and I will find the thing I could have done better (unless I can PROVE it wasn't better). It may not be the correct all the time, and it may not be possible to PROVE what was better, but I'm sure it will make me a better player.
You will have a hard time convincing me that luck is 10% as important as skill is in Dominion, even if you are right.
On a related note, these same people often tell me that I'll be completely killing them in a game, but still thinking it's close or I'm behind and playing as if I am. Granted, this is sometimes because I've miscounted how many Provinces I have (oops), but I believe this attitude improves game play as well.