I think Sean is a lot like Sergio. The putting was always the problem. After a while it creeps into their long game, because they think they have to hit it stiff to make birdies. I know every player has strengths and weaknesses, but imagine if Brian Gay putted for either Sean or Sergio. Every great player was an above average putter.
From the statistics I've ran, outside of '09 O'Hair has never been a great ballstriker. I wouldn't call him quite 'great' in '09 either, probably 1 level below that which to me is 'really good.' Other that that he's hovered around 'above average' to 'decent' to 'average' as a ballstriker over the years. His putting has usually been in the average to below average and his shots from 0-20 yards around the green is probably his weakest part of his game.
Sergio OTOH, I tend to agree with although he struck the ball poorly by PGA Tour standards last season.
As far as every great player being an above average putter, Phil has struggled mightily with his putting in many different seasons and has won majors those seasons and been in the top 5 in money. He's more the exception to the rule because of his game (hits it long, very underrated irons player, great around the green). From analyzing statistics, I think in order to have a great year on Tour, one could probably do it with average to slightly below average if their ballstriking is good enough and if they hit it long.
From a statistical perspective, one of the advantages of power off the tee is that one can putt worse and 'get away with it' to a certain extent. Right now Bubba Watson's putting stats are poor, but he's having a great year. It helps when Bubba is #2 in distance and #65 in driving accuracy (last I checked).
3JACK