Who uses their "main" Google account for these one off services anyway? I can't imagine it would be too popular to keep pseudo-anonymity. you don't want to post lol cats from the same account you use to send your resume, I would think.
Is that a rhetorical question? Probably 99% of people playing this game who sign in using Google use their main (only) Google account. I'm sure it never even occurred to them to make a second one for something like this -- that would just be a hassle.
