>> My first post in the thread was simply, why limit to just those two.

If people are concerned about fragmentation, why limit it to just the phone. There's far more experience with the PC and far more fragmentation as well, but Windows still seems very popular. I'd also say that in the device manufacturers' shoes I'd do everything in my power to keep the smartphone as a unitary device like a traditional cellphone rather than something millions of users can brick and otherwise turn into a support nightmare. I'm very sure the telephony providers who choose and subsidize handsets feel the same way. What you call "orphaning" may be a very good way to stop people breaking their phones and clamoring for help- after all, a reliable phone is more important to many people than their PC.