The shortest route will always favor the person with the most keys and the most trust. Who invariably will figure out that he/she can make money getting more keys and more trust. Which lucky for us their are both a finite number of persons and a finite number of keys that will be signed by each key. We end up with a pyramid scheme.
Where the more trust and keys you have, the easier it'll be to get more trust and keys.
:.:.:
The problem is capitalism. In all honestly we'll likely see the PGP network end up in the hands of banks. You want secure access to you online account? Sign each other keys. Now the bank has a 5 million person strong trusted key. They'll sell that trust naturally. I trust most tech companies enough not to instantly monetize the PGP web, but some would.
Likely some tech company attempts to monetize it, they get yelled at. They stop. Another does, nothing changes so people accept it as the new norm. The arguments made it allows for faster page loads, easier access. Nobody says a word after a year.
With PKI, you can't choose the root CAs. Today, Verisign abuses the shit out of their market dominance to price gouge certs, and I have no reason to ever trust that company with anything, they don't give me a reason to, and they almost certainly have their root keys in the pockets of groups like the NSA.
So if I don't want to run my WoT through Google, I could choose not to. For the average user they shouldn't care, but I would at least have the choice. Right now there is none.