You raise a good point, and in order for this to work they'll need to ensure a full suite of emulators are available for testing. Android already provides an emulator [1] that can be configured to match the target device, although I can't speak to its quality as I have not used it. Windows Mobile is in a similar position, and its SDK provides emulators for every phone you would want to test on.

Phones differ so much in form factor alone that you really need to be testing individually for any phone in your target market anyway. Its a huge time-sink to be sure, but you won't be flying blind.

[1] http://developer.android.com/guide/developing/tools/emulator...