I know what you're saying Lunar. Post count=ammount of posts you've, well, posted! lol
But people will never get over the assumption that more posts=more respect/power/fame/whatever.
So, allowing it to increase post count will only up the number of spam topics by like 500 times the normal ammount, which is worthless and not needed. A "spam" post is also not concidered a "true post" by many.