Ford is the most aggressive company in marketing their trucks, and is willing to put a huge number of them out on their dealer lots.
2014 - Jan-Jun - units sold
Ford - 429,065 - 0.3% increase over the same period in 2013
Chevy - 282,775 - -0.7% decline
Ram - 239,481 - 18.8% increase
GMC - 110,679 - 6.2% increase
Toyota Tundra - 88,398 - -7.0% decline
Do realize that most of those trucks do not tow, especially as anything as heavy / large as an RV. Large numbers of truck buyers want a pickup, but want sedan type gas mileage. Ford understood this before the other companies, and has done a great job marketing their Eco-Boost.
The only thing the numbers really reflect is the strength of the manufacturing company and their marketing commitment to the pickup.
Being in Texas, I see a lot of pickup. At times more pickups than sedans. And it's about 4 Fords, 3 Chevy/GMC, 2 Ram in ratios.
Camp hosting I see a lot of rigs - the average numbers run about the same. Only when you get into the 17,000 pounds or more range of fifth wheels does the Fort 450 / 550 become the dominant choice.