Actually, a high percentage of markets have at least one VHF-High channel (7-13). The move to more UHF stations had a lot to do with the economics of having to broadcast both analog and digital signals during the transition period.
Now we have a new fun and games period developing in the next couple of years. The FCC just completed the mandated spectrum auction this last March. The current UHF channel assignments go up to and including channel 51. The newly implemented channel allotment will only go up to channel 36. Therefore, 60+ percentage of the stations will be changing channels again. Some will be going off the air for good. Many more stations will be moving into the VHF-High channel allotments. This will take places in stages over the next couple of years. UHF only antennas will not cut the mustard in many areas by the year 2020.