Yes, it is decentralized, but regarding to the number of available public nodes it's not really the case currently. I guess it has to do with the many updates in the recent weeks and the fact that a blockchain replay for a full node takes several days...
I think we need kind of a reward for people who supply the network with a stable RPC node. The hardware is very expensive (If I could afford, I would start an own node) and not all top witnesses are providing such endpoint to us, so their witness rewards go into other things. As more and more users are joining the Steem network, this problem becomes more and more important.
Thanks for your many great votes btw ;)