These trophy statistics are interesting. It's crazy how many people buy games and don't even come close to beating them. I play a lot of RPGs and you look at the trophy stats and for most of them under 30% of the people that start them get the trophy for beating the game.
that's cause besides the trophies related to the story, devs have to add in trophies for replay value....like beating the game on harder difficulty levels, doing certain actions, doing something however many times, mp trophies, etc...and unless they are a trophy hunter, most people don't care about doing all of those things after they've beaten a game...some people just like beating games, some just like collecting trophies, and some are in the middle (i'm in the middle)...
also, devs get a trophy point total to mess around with...it's up to them to decide how they wanna distribute those points...which can determine trophy completion percentage for games depending on how many trophies they stuff in...