Doesn't make sense though ! I would prefer this concept if they have it on the amazon.com homepage. I would hate to give my mail address. I have a feeling this was done in response to Google Wallet.
http://blogs.zdnet.com/security/?p=554
It looks like the gmail team has created a fix and pushed the fix. It suggests that you keep checking your filters to see if you been rigged as the fix wouldn't fix it (pun intended).