That 1-2 point gap crops up in a lot of settings - not just programming, but writing and public speaking and many others.
The common element seems to be hidden process followed by a finished product. Your peers see the code you write (or essays, or speeches, etc). You see the writing process, with all its inevitable inefficiencies and foolish mistakes. No one sees Obama stumbling over his speeches as he gets dressed in the morning, they just see a skilled final delivery.
So without more context, I would guess that you and your peers are rating different things. You're rating every stage of your development, and they're rating the results, or at least the commits.
The common element seems to be hidden process followed by a finished product. Your peers see the code you write (or essays, or speeches, etc). You see the writing process, with all its inevitable inefficiencies and foolish mistakes. No one sees Obama stumbling over his speeches as he gets dressed in the morning, they just see a skilled final delivery.
So without more context, I would guess that you and your peers are rating different things. You're rating every stage of your development, and they're rating the results, or at least the commits.