|laziness, impatience, and hubris
Hmm, I think you're missing how it works.
Addresses are not rotated as a matter of course. An address optionally can be rotated if the correspondant exposes it or starts sending unwanted mail to you. This is an exceptional circumstance, and in this exceptional circumstance Segmail is no better or worse than any current solution.
There is no concept of most recent address. The extra solution for exposing an address to the web and automatically rotating it is tacked on, and not the core of the solution. This extra solution is non-ideal, but still better than current solutions - or put another way - it can fall back to a current solution.
I'm sure DSPAM is very good, but for some, any possibility of a false positive requires the maintenance of a junk mail folder. Some would like a solution where there was no possibility of a false positive, and hence no need to maintain a junk mail folder. Or in the abstract, I don't want a computer deciding which messages I want and which messages I don't.
I have to take a closer look at SPF. I thought it was a statistical solution. Thanks for pointing it out.