Depending on personal preference though, this could be a misleading statistic. Demos, not for resale, player's choice, variations, limited editions etc are all a part of a system's library.
I was thinking about that sort of thing too. Maybe there could be two percentages; one that includes variations and one that doesn't. That way someone who wants EVERYTHING will be able to see how far they are and someone who doesn't care about variations doesn't have a skewed percentage.