When will you guys get it through your heads that 'distributed everything' doesn't work. Central authorities are needed to mediate and ensure everyone is on the same page.
Those central authorities are welcome to join in, and become highly valued nodes in the WoT.
Central authorities also come with the risk that they can be compromised, but its far easier to deal with one compromised CA than several billion.
Aha, now I get it... could it really be this simple? Are X.509 advocates merely bad at math? The terms in your risk assessment formula are wrong.
If a signer has a probability p of being accurate/trustworthy, then the chance of its attestation being correct, is p. That's how X.509 certs work and of course you understand that very well. Cool. With PGP, if signer1's probability of being accurate is p1, and signer2's probability of being accurate is p2, then the chances their joint attestation of an identity is accurate, is 1-((1-p1)*(1-p2)). Dude, that's a number which is greater than either p1 or p2.
For example, say you think it's 90% likely that Verisign is telling you the truth about a key belonging to a certain website. They're the one and only signer for some website (because one signature is all this shitty tech can handle), so you think it's about 90% likely you're talking to that site, and 10% likely you're talking to the NSA. If that's your estimate of Verisign's reliability/trustworthiness, then 90% is the best you can do with that tech.
Now let's say we upgrade from that garbage to 1991 technology: the PGP WoT. Suppose Verisign and CNNIC have both signed something, and you think Verisign is 90% reliable and CNNIC is 60% reliable. (Those sneaky Chinese bastards!)
You're 1-( (1-0.9)*(1-0.6) ) = 0.96 , that is, 96% confident that you're talking to the website you wanted to, and 4% worried that you're talking to someone who is involved in a join US-China conspiracy (which, now that you think of it, is less than 4% likely to really occur). You have just wiped the floor with X.509's security performance.
Suppose I signed it too. You don't know me. While it seems absurd at first that I'm less trustworthy than the Chinese government (they're known badguys; I'm merely some internet asshole) at least you know something of their loyalties or lack thereof, and very little of my competence and motivations. It's reasonable to assume I am probably more likely to conspire with your adversaries than they are. Some guy with US government might be holding a gun to my head, right now! So you decide to only trust me 1%. Ok. Guess what? You can work with that!
Now my super-weak signature is on there. You trust the identity 1-( (1-0.9)*(1-0.6)*(1-0.01) ) = 96.04%. My super-weak nearly-completely-untrusted attestation made it stronger.
This is why were totally wrong when you said one compromised CA is easier to deal with than a billion. A billion compromised CAs are easier to deal with than one. Distributed authentication is more fault-tolerant, and we're now in a situation where the mainstream finally "gets it" that the faults really do occur, rather than it simply being a tinfoil hat thing that cypherpunk SciFi authors pretend to worry about. X.509 is based on the idea that Verisign is telling you the truth 100% of the time, and cannot model the idea that you think they sometimes fail. PGP, on the other hand, is based on reality: that grey world where sometimes things work and sometimes they don't, where you sort of trust some people some of the time, etc. You know, that world that you actually live in.