I think the difference between Google's DMARC policy for gmail.com and google.com says it all:

  bcrl@home:~/electronics/vrm/lm5017/test-lm5017-isobuck$ host -t txt _dmarc.gmail.com
  _dmarc.gmail.com descriptive text "v=DMARC1; p=none; sp=quarantine; rua=mailto:[email protected]"

  bcrl@home:~/electronics/vrm/lm5017/test-lm5017-isobuck$ host -t txt _dmarc.google.com
  _dmarc.google.com descriptive text "v=DMARC1; p=reject; rua=mailto:[email protected]"