A centralized host can't ever be the only reasonable option for trust. They can be manipulated, technically or socially, and that makes everything vulnerable at once.
The Web PKI is built around centralized roots of trust, and survives because of concerted efforts to make those roots resilient, trustworthy (in terms of underlying ownership), and publicly auditable (with mechanisms like CT).
To the best of my knowledge, there has never been a successful decentralized PKI. Even the most successful uses of PGP are not decentralized; they're essentially private PKIs maintained by a small set of presumed trustworthy maintainers.
PGP absolutely is decentralized - I can trust or distrust key X without communicating at all with any external PKI.
I agree that's not all that useful on a global scale - it essentially degrades to the current PKI setup then, because validating everything is expensive and doesn't need to be done by everyone every time to get nearly all of the benefit. But it is a significant difference for individuals making individual decisions.
Both are useful.