Note that the above figure that it takes 3.5 times more towers to operate GSM than CDMA is based on the cited page's metric named "maximum talk range from a tower (pls. note you will need a carkit for both to achieve these numbers)". I doubt carkit ranges are an effective measure of number of towers needed to cover an area.
More important limiting factors on tower coverage are issues like how many channels can be used per slice of radio spectrum, and how many slices of spectrum are created out of a provider's licensed spectrum bands (at least in America), which is affected by relative size of the provider's licensed spectrum are in a given market, etc etc.
To provide enough coverage in non-rural areas, a provider puts up more cells in an area with a smaller transmission radius, no matter which technology. So, the limiting factors become how many towers (cells) in an area, and how efficiently the technology uses however much radio spectrum it has.
As far as I have heard, CDMA made a great many promises on its future abilities, but has not grown as much as GSM has. I'm sure that can be disputed, but my main point here is that the above post is incorrect in its main point. It's also funny in that the link cited seems to be much more in favor of GSM than CDMA. And I can definitely say from experience that CDMA voice quality leaves a lot to be desired in what I've heard.
--Jim