If I were to hazard a guess at their motivations, I'd suppose that they chose 3 symbols -- and those particular three -- instead of two to ensure that you'd never send the same symbol twice in a row. This might make timing recovery on the receiving end much easier. You get away without a clock on that end. And fewer parts in the IR receiver means more budget for rosewood veneer, and leave the hard work to the optional (and added cost) remote control.

Glad to hear you found some useful info on the B&O stuff. Sure hope it pans out.