Not really and still learning. I guess everyone that has Bitcoin Core installed has a full-node?
What I mean is that surely blockchain.info wallets work with some kind of modified bitcoind. and my question was how many bitcoind full-node clients do they use to maintain so many users?
I don't know why, but now i can't find any information on their site.
Before, it was here -
https://blockchain.info/connected-nodes . But link is dead.
Also, you could see number of nodes in the bottom of the web page before, but now is nothing there.
I'm also unsure of how blockchain.info "wallets" actually work.
It's connected to full nodes and pushes transactions through them (in simple).