As a side note, the frequency of offenses does not dissolve whether spam is spam. You can say it doesn't do harm as a whole but that shifts the argument away from the fact that spam is an ongoing effort most people try to avoid from happening at all.
Twitter is constant self-promotion - you constantly share your thoughts and views. And somehow that's fine and you get followers. Is tweeting spamming? Besides, see the other comment with the chart attached.
Using Twitter as a counter example doesn't fit here because as a company they don't share that view but apparently the subreddit you reference in your original post does
Methodology behind the chart: http://www.reddit.com/r/dataisbeautiful/comments/2rv76z/oc_r...
The 10% rule is archaic, from a time where undisclosed self-promotion was rampant. Now that it's hitting false positives, it needs to be revamped.