I think in my dotnet client/server system, we use WCF duplex extensively, meaning the server can push updates to the clients. Each client must subscribe though. I think this is exactly event-driven as you said.
I remember that if I put a break point in the client’s updateReceived() callback method, it gets hit automatically, without the client polling the server.
WCF duplex is a standard and mature feature in microsoft WCF.
The server endpoint uses https, and I believe it’s a web service.
Is it possible that the server push is implemented actually by client poll under the hood? I don’t think so. There’s a polling duplex ..