A: Because Bob lives in alternate universe where you still define technology options around IBM offerings like it was 1987. His new financial startup is like an early cloud computing customer -- entering into a time sharing agreement with his local bank to utilize their excess MIPS via ISDN. :)

If you're using a stack dependent on 3270/5250 connectivity, you're better off using stuff like this. IBM supports it end to end, and it will support all of the functions in the terminal without code changes or other workarounds. Nowadays increasingly fewer people actually know what they are talking about with these technologies, and you're better off touching as few things as possible!

Mainframe and midrange people probably find the relatively recent NoSQL movement similarly amusing. Fast KV store seems important to you, eh? Just figuring that out? What if it came with OS level awareness?

"Bob" is using some kind of "old iron" possibly emulated on mainframe and communicates to it with a retro terminal client (5250 ?).

So... do brokerages use telnet in the wild?

Well, I know of at least one iSeries (AS400) software vendor who does use it in the wild.

there are many trading floors which are still run by IBM mainframes which do still use telnet