While I am a huge Git fan, I completely understand their decision to go with Mercurial. It has better documentation, better cross-platform support, and a similar feature set. Git is improving in all these areas, and I use Git for my personal projects, but Mercurial does have its advantages.
Well the google code support was started long time before Python started looking for a DVCS.
If one had an influence on the other it was probably the other way round.
I wouldn't count on it. Internally Google uses Perforce for version control (and IIRC git for some public-facing things), and it's been noted that Google's Python style rules and procedures are quite different from Guido's (their style guide actually goes against PEP 8 -- easy way to spot open-source contributions from Googlers, though).
