According to a conversation I had with Paul Buchheit (paul here at HN) in the past, GMail spam filters are heavily reputation based, which leads me to believe that Bayesian filtering is not a first line of defense, and likely would be specific to each mailbox rather than universally applied. So, if it's happening to everyone, then it's a universal rule at GMail that's doing the filtering, and thus I would guess not heavily based on any Bayesian results. But I might be wrong, GMail spam filtering may have changed dramatically since paul worked on the project, or I may have simply misunderstood his explanation.

But pg did invent the most powerful recent spam fighting technique. I'm not sure why one would say the description provided in the essay isn't the same as inventing it? Certainly Bayesian analysis existed long before the essay, but I think it's safe to say that the inventor of the airplane was no less its inventor because the internal combustion engine existed before.