"Google makes money precisely because the web is centralised"
I see it exactly the other way: Google makes money precisely because the web is decentralised, and hence you can create an invaluable service by crawling it and creating a centralised search index.
That's another way to look at it, but you're using decentralised to indicate there are many large nodes- I would say that's simply distributed. I'm using centralised to indicate that communications are via those large nodes, which mostly don't communicate with each other.
It's client/server on a massive scale. Just because the servers are public, doesn't make it decentralised.
I see it exactly the other way: Google makes money precisely because the web is decentralised, and hence you can create an invaluable service by crawling it and creating a centralised search index.