It depends: in the US not many people buy unlocked devices; in the rest of the World a lot.
Rechargeable SIM cards are very popular in Europe and people swap them from carrier to carrier depending by the ongoing deals offered. And again the biggest issue is perception: I would be very upset if I paid �500 for a device and discover that I cannot use in its full potential.
I do not understand why it is so complicated for MS to state something about a coming fix for it.
Point well made. Microsoft should have included this from the get go.