For what it's worth, at work, I've taken to
putting an FT232 (or 2232
or 4232, depending on how many ports) on new boards instead of real
RS232 for the simple reason that our clients have a hard time finding
PCs with serial ports and are too clueless to buy proper serial
adaptors. Plus, a mini-USB port takes up a lot less room on the panel
than one DE9 (let alone four), and the chips generally cost about the
same as a decent RS232 level converter.
What I would prefer (at least for devices that don't need the high data
throughput of USB) is that the device has an asynchronous port brought
out to some suitable connecotr and that said devie is shipped with a USB
interface cable that plugs into said connecotr. And of course that all
this is documented.
That way, users that prefer USB and/or have modern PCbs can just plug in
and go. I can make a level shifter, plug that in, and conenct said device
to an RX232 port. Bust of all worlds...
-tony