Had this thought today.

Symbian; Maemo; MeeGo.

The last two are quite distinguishable from each other in all aspects.
Symbian on the other hand was split into various guises/versions to suit the type of budget the phone was aimed at.

They had a version for the cheap ten-a-penny phones, a version for mid range and a version for smart-phones.

What about WP7? Is this thing "modular" so to speak, can features be removed or added or is it as it comes?
I can't imagine Nokia releasing phones for the lower end of the market with the same O/S as the smart-phones, because I can't see that hardware features are going to make that much of a difference to price point.

Just a thought