what DO folks say about it?

I don't want to argue semantics about the definition of "duplex". To the extent that Google Voice is not quite full duplex, what makes it not quite? Is it a property of the application, the connection, or the hardware? A "yes, but ..." or a "no, but ..." would be fine.

"Duplex is not completely full duplex —you have to wait slightly longer for the other person to shut up"
That's called "latency". It's pretty independent of whether I can interrupt someone.

The "objections" here don't really answer my question. Perhaps you can point to a "prior discussion" that is less than three years old. I've looked around on the web, and haven't found much of anything useful.