So I first thought there was a bug with the graph, and then I though: do all these BTC not being paid every day come from many users with very small balance? I know I've had one for a few days. I guess you'd need quite a few users with a balance less than 0.01 BTC (~8000 ?).
There are something over 32,000 different id's so yes, it's a little dust for each of a lot of users. H2O has been lax in cleaning out the penny pile.