A. Those are the frequencies that are allocated by international treaty and FCC regulations for this general type of service; and
B. The circuitry and firmware was already designed; and
C. Why not?
If I am understanding you correctly, are you saying that this technology was already set and stone before the Vantage Vue came into existence?
No, that's not what I am saying.
A. By international treaties and national FCC regulations, only limited frequencies can be used for certain purposes. Most of those frequencies must have specific licenses from the FCC. Some can be used "without license" for particular purposes like this. This 902-928 MHz band has a lot of restrictions, and devices within the band must be thoroughly tested by approved laboratories and then approved (registered) by the FCC. That's why you will find an FCC registration number somewhere on the device. As on the VP2. Before the Vue.
B. Davis already had designed this circuitry for the VP2, had it tested, and registered. It wasn't set in stone - they could have redesigned it. And re-tested it themselves before submitting it to a testing laboratory. But (presumably) taking a design that had already been proven, and submitting it for registration testing, would save a lot of time designing and testing.
C. Given the interoperability advantages, and the saving in re-design effort, why would Davis deliberately do a different design that was incompatible with existing VP2 hardware?
Does that make sense, Andy?