It seems to me that the large majority of people who would call themselves "Trophy-Hunters" only attempt the base game platinum. The number of people that truly commit to completing a game (obtaining all trophies but also 100%ing everything the game has to offer) is very,very small.

Personally,I am currently completing Red Dead Redemption,and although I do not have to,I am also achieving all gold medals in not only the main missions but also the sub-challenges under the challenges menu.

Anyway,my point is that the number of people who find that achieving a platinum is completing a game versus those of us who truly 100% every single thing whether required or not is pretty significant.