I was looking at boxing D3 recently, and ordered four authenticators (not sure how long the one I have will last).
Surprisingly, each of the accounts is still protected by the original authenticator.

I had five b.net email accounts, each protected by the same authenticator.
I later rearranged my wow accounts, so each of the first two b.net emails had five wow accounts.
Despite having no game accounts attached to the 'C', 'D' and 'E' b.net emails, they're still protected by the original authenticator.

I had not realized they had gotten rid of the auction house and real-money auction houses.
There's much less incentive to go after accounts, without the chance of monetary gain.