According to Baseball-Reference.com, there have been a total number of players in the history of MLB of 17,761. It doesn't even specify on there that that number doesn't include pitchers, unless I'm missing something. But even if it doesn't, Moyer has pitched to 1,419 hitters according to the link posted earlier.
1,419 / 17,761 = 8%.
So, that stat is simply astounding, and in fact is not BS.
http://www.baseball-reference.com/