I think an added benefit of this middleware software, would be allowing it to report to multiple applications at once. RS232 doesn't really like it when multiple programs are talking at the same time. So this program would be the master, and the only program that's making an actual connection to the box using any method supported.
It looks like they have the ability to report data to their webserver using some of their software, and you could also have your home automation software talking to it at the same time. Thus not having to chose not to use their web server for live readouts just because you want to integrate this with your home automation system.
It's possible I'm misunderstanding, but using the supplied virtual com port you should be able to skip the tray software completely and talk directly to the serial communication.
I've looked over the PDF document that I got from Paul, and it looks like it's the same RS-232 protocol when you talk to it over USB, Zigbee, or Ethernet. Its likely that their Ethernet solution is going to be an Ethernet gateway that requires some sort of software running on the PC to make a virtual com port to Ethernet device that still accepts the same serial communication.
Please someone correct me if I'm wrong!