Why is Verizon Wireless Reception Poor on the East Coast?

Does Verizon Wireless use a different frequency on the East Coast vs the West Coast?  We have also been receiving a great number of complaints for Verizon since the iPhone and iPad 3G CDMA devices have been available on their network.   On our Verizon Dead Zones map which collects anonymous complaints from customers has been receiving a greater number of coverage complaints proportionately in Eastern States like New York, Florida, Georgia & New Jersey.  What is the the explanation for this?  On the West Coast we tend to get more AT&T Wireless dead zone complaints versus Verizon.  Is this because their is a great concentration of iPhone users in the West Coast cities like Los Angeles and San Francisco?