I got your point. The conclusion is not important, but the rational we used to reach the conclusion is important:
"Synchronous architectures are more appropriate than asynchronous architectures in applications where the sender and receiver must participate in a message
exchange, and the sender must respond to the receiver in a limited time frame."
Go back to my initial statment. For the stock price, traders definite need it in a very timely manner to make their decisions. Whether buy or sell or even no further action is trivial.
As to the cc authorization scenario, you provide a very good reasoning. I had an experience when people took for granted 'something' must be within a transaction synchronously until the performance brought down the server's knees and no tunning could make any improvements further. However, cc authorization, I guess, is a different story. Most cc servers should be VERY powerful and react instantly. Anyway your reasoning makes sense. Maybe your business model will gain more popularity in the future. As I said, I don't care about the final conclusion. Thanks for participating in my discussion.