The former (booking a table) is much more "constrained", as in the conversation would most likely not go into much of a tangent, because there are only so many responses to a statement like "book a table for four at 8pm" (8pm is full, 8pm works, etc).
Whereas asking someone how their day was would give the "victim" a much bigger breadth of responses (and additional questions!) that would cause the AI to stumble and fail to give a satisfactory answer. That, and running this 1,000 times simultaneously so that no one person would be able to intervene to "help" the AI would just be a highly unscalable operation.
So yes, huge difference.
Duplex is interacting with a human and that person has no idea its a computer on the other end. Yes, Duplex is limited as it stands, but what is there to make you think something as described in grandparent post won't exist in ten years?
In terms of NLP, the Duplex seems hardly that much of a jump. The main improvements seem to be on the speech part.
I would say that there's a market for that. How long before rough agents implement good AI for their operations? How long before we implement defences against AI?
If an AI can do that, then singularity is definitively reached.
Imagine how a 'long con' works today: a scammer befriends a person online through a video game or social platform, and develops a rapport with them over the span of days, weeks, months. After some trust has been gained, the scammer then requests money from the victim. Does this happen a lot today? I don't know, but certainly one reason it doesn't is the economics of the scam. Who wants to spend a significant period of time gaining trust just for the chance of a payout?
AI is going to flip this on its head. Rather than dedicating hundreds of hours of a scammers time, a scammer could instead use a system like Duplex to befriend hundreds or thousands of victims simultaneously. Let it run for a few months, developing a strong rapport with the target, until the AI finally requests some money from the victim.
Yes, duplex is for completing specific tasks, but how much of a difference is there between "Duplex, book a table for four at 8pm" and "Duplex, ask my victim about how their day was"?