i think its okay as long as there will be another nokia lumia like 922, 910, 9xx . All of these will perform same as 920 so verizon will have an t mobile will have.
Its exclusive to Telstra in Australia too which makes it hard for Telstra haters to get their hands on the Lumia 920 including me.
Only 6 months? that's ages in phone lives. I hope Nokia gets paid well for carrier exclusivity as not being available on other carriers can put a lot people off the phone.