chessmaster vs. chess.com

I own the 10th edition chessmaster (among others) where josh waitzkin is prominently featured and many grandmasters are available for light perusal.  I notice that my rating on chess.com is significantly higher (100-150 pts).

Even when i factor in winning on time, the 3 day move time, and your average human blunder, chessmaster still presents a major challenge that chess.com does not.  Could this be because the software pertains to a more rigid execution of opening sequences, or a more mathematical approach to matches?  Perhaps it is because people are more likely to deviate or miss particular arrangement avantages due to basic human perception?

I've been wondering about the gap between my chessmaster ranking and chess.com ranking for some time now.  It seems directly related to methodological learning methods and ranking systems.  I generally learn by playing, not by persistent study.  maybe it's simply a different learning curve?

any advice would be gratefully appreciated.