Lynn,
I don't like to generalize, but...of the number of high scores I witnessed today, I would say simply, that a large majority were caused by poor swings compounded by even poorer thinking.
Merion is not a course that you can force shots on. Even with poorer ballstriking, if you manage you game and your misses, you can still get around. You'll make alot of bogeys for sure, but you can certainly avoid the others.
When I see the best players play courses like Merion, they are obviously concerned about where to hit the ball, but also quite concerned about where to ABSOLUTELY NOT hit the ball. Unfortunately for them, I saw a lot of guys in the Am that needed to pay more attention to the second part of my above statement.
While many courses penalize bad shots, Merion does so to a much higher degree. With the tough hole locations, and the great contours of the greens, if you compound those swing errors with poor judgement, you then get into big numbers. This is what I love about Merion. There are holes that are just flat out brutes: 3,5,6,14,17,& 18. Then there are the many holes that appear easier and can offer some birdies, but at the same time you can make a double bogey quicker than you can blink.