Well I knew coal fired plants make over 50% of the electric power in the U.S. so 52% is believable. In fact, this D.O.E. link mentions that and a couple other interesting related facts
Department of Energy - Electric Power
This cost info is probably the most significant reason why coal is popular, though the cost of cleaning coal, or processing it like in coal gasification is not included in these costs:
The Energy Information Administration has this nice pic:
Figure ES 1. U.S. Electric Power Industry Net Generation, 2006
Natural gas is projected to be the largest growing fuel segment for electric production in the U.S. for the next 20 years or so.
I'll throw another interesting "fact" I read recently...I'll have to find where and if it's true since I didn't check it out... but it said there is more radiation emitted into the atmosphere (per kW produced) from a typical coal burning powerplant than a nuclear plant. Apparently the natural radiation level in coal is the reason why.