Depends on the device. They're not all identical.
True.
No, but everything seems simple when you aren't aware of the details. It might be "better" in a technical sense but from a cost perspective there's little reason to create such modularity. Why are you thinking that the work needed to support this would cost less?
It just seems like a standardized interface would make for faster and cheaper development. Once you design the board, manufacturing is easy. If HTC doesn't have to engineer a new interface for each phone, that saves them time and money. If Qualcom designs their processor/radio combos with a standard interface, that saves them time and money.
Manufacturing is (from a time perspective) is cheap and easy. Design/engineering is expensive.
And locking it down to one band wouldn't be beneficial either. It would defeat the point of the modularity that you propose as the OEM's would have to produce different models for different bands.
Not really. Antenna design is pretty straight forward, here. Just make the actual antenna bit roughly in the middle of your frequency bands, then solder in a few capacitors or inductors to electrically tune the antenna. It's not as if these things are running at 2MHz and need a 30-ft dipole to operate.
I realize I'm simplifying the steps involved, but I'm doing it for the sake of argument. I'm not trying to shift the cell manufacturing paradigm, or anything, I just wanna know why they can't just design one phone, then slap the appropriate radio into it. Mostly, I just want a damn DincS or Dinc2 or whatever they are gonna call it.