My experience is very similar to yours. I think there are probably two reasons. First, it is generally agreed that ratings on this site are inflated. You really can't compare your chess.com rating to some other rating, but it is a way to measure how you are doing if you look at your stats page. Second, I have read the suggestion that Chessmaster "opponents" are somewhat better than rated, and I believe that is also true.
chessmaster

I think sometimes your rating on chess.com goes up thanks to people who just make a couple of moves than let times run out. Nevertheless it's a victory. A computer it's always there human not..... so.
I also have an old chessmaster version running on my mac, it'a a great program I think and over time it's been a good source of training for me too.
when im not playing live chess i play against my computer and also chessmaster i can beat both on really low levels but never beaten it above the rating level of 1250 most games go to end games. but on chess .com have one against so many high rated players i class myself as a very low 1400 player so my am i winning games against human players.