Stienman, I don't know where you were pulling your numbers from, but I'm pretty sure the sun doesn't shine there.
I happen to work for the company that provides all security services to most cellular towers in Belgium - since they're all forced to share towers here, the owner of most sites insists on a security guard on site for any works done, so they don't start sabotaging each other (not that our guard would know what cable they're pulling loose or cutting or whatever, so it's entirely useless, but don't tell them).
There are, on Belgacom-owned lands (the company that used to have the phone monopoly in Belgium), over 5,000 separate towers in Belgium. Of course I admit that's a big difference from the US - we're a fucklot smaller - and since we live much closer together, one tower does cover more people. And I don't mean to say that has nothing to do with anything.
However, the open sky has much more influence on the strength of your signal - yes, if they're far away you'll get more lag, and obviously if there's a lot of people in between you'll end up with crappy reception, but a tower with a decent-powered transmitter could easily cover the entire surface of Belgium, if it were entirely flat (it isn't). It'd only serve maybe 1% of the population, but that doesn't alter the fact that you'd have a signal. There's literally no way, except by satellite, to get reception throughout Swiss without a separate pole on pretty much every other mountain top.