63% after 20,000rolls means the probability is greater than 1/20,000
I calculated "63% after 20,000 rolls" exactly from 1/20,000 probability 
It's how probabilities work: if probability of an event is 1/n, and you perform n trials (and n is a big number), usually you'll get ~ 63% probability of getting an event at least once, because 1 - 1/e ~ 0.63 (if you would do the math, it's easy to show this is the limit when n->infinity).***People that have a lot of affiliates don't even get one of their affiliate to roll 10,000 :
Amount won-number of affiliates
6-0.25252830 BTC 7748
7-0.20269780 BTC 1059
8-0.20220446 BTC 1182
9-0.19664634 BTC 575
The important number here is a total amount of rolls by all affiliates, if most of those 8000 affiliates done just a few rolls, this isn't so strange.Amount won-number of affiliates
6-0.25252830 BTC 7748
7-0.20269780 BTC 1059
8-0.20220446 BTC 1182
9-0.19664634 BTC 575
It is possible that those affiliates only did a few rolls each but my affiliates still do more than 1roll/each/week after 2months so I presumed they got similar stats but all affiliates may not be created equal
You are right for the 63% I remembered it being 53-58% but your math is correct here; 1/20,000 is pretty good, let's roll!
Can you calculate how much he get from publicity per roll compared to how much he gives away?