I agree, they will still have overall better coverage. T-Mobile claims to offer coverage to 96% of Americans (though a significantly higher percentage of that is EDGE or lower), while AT&T claims something like 98%, and Verizon 99%. This goes a long way towards closing the gap though.
Ya those % numbers just mean how much of the population can make a call on their network or by having service with them [be it on their own partner network]. Wait till the day they start advertising "Data covering 96% of americans" lol that will be the real deal.