How are payouts determined in NASCAR? Why was Dale, Jr. paid less than worse drivers? ?

Dale Earnhardt, Jr. finished 11th and was paid $108,300, but 17th place Ryan Newman got $133,950, 19th place Robby Gordon got $119,208, 24th place Sam Hornish, Jr. (a rookie with no Cup wins ever) got $132,625, 25th place Elliott Sadler got $115,095 and Reed Sorenson finished 39th and got $108,564. That does not seem fair to me. Of those only Newman has a win in 2008. Hornish and Sorenson have never won a Cup race. Are their sponsors more generous?