You also have to factor in power/HAAT/population/etc to get the most for your coverage area. For example, NYC stations cover a lot of population with lower powered stations than most of the rest of the country. The spacing of NYC stations seems to be the shortest allowed at the time, also.
Makes sense; take a map of the U.S. How many 100kw stations would it take to cover it? How many 3kw stations would it take to cover it? Mix all that up with growth patterns and predictions, and you really begin to have fun.
It's almost like the "solution" to all this would be to sandwich in a bunch of translators. Wow - what a concept.