That is pretty cool, and not very many people can do that. It's interesting to see accumulating payouts and it's one way to illustrate the difference in payouts from day to day. I'd argue that none of the balances accumulate over time but are really the same value in coins that move from one to the other and eventually to payout.

Edit: It is interesting to note things like on sep 21 there were a total of ~1380BTC of accumulated immature and 1360BTC balance. The difference of ~20BTC is maybe mostly invalid blocks and so on.  Where did you get the lifetime accumulated number of unexchanged and immature?