I would like to respectfully disagree about spam on Yahoo mail. I have so much spam there, you won't believe. And what irks me the most is that a lot of it is easy spam: viagra, etc.
well, you have one anecdotal data point with two different email addresses, while I was providing a fact on 10,000 users with the same email addresses on both platforms.
my guess, you probably had the y email much longer than the g one (yahoo mail is a decade older) and you posted that email in too many geocities guestboards. do the same with your g address and report back in 10 years :)