I paid 50HKD/month for "50mbps" cable internet (some special deal at the time). What a joke. I got 50mbps torrenting and about 0.5mbps from anywhere outside Hong Kong.
The OP's "It's a cell phone carrier's dream; one tower can potentially reach nearly a million people." is the exact opposite of true. Frequencies used for mobile communication are limited and with that the total bandwidth of a cell site is limited.
This is the main reason new G's are coming out, 3G is packing many more bits per Hz then 2G was, and 4G is doing yet more.
New frequency bands are released for mobile communications to further alleviate the problem.
Network planners have to install more and more cells in dense urban areas and be careful not creating too much noise on the frequency as they have to reuse frequencies and codes.
In a place like HK skyscrapers are creating lots of problems with signal shadows and reflections.
Major office buildings sometimes have (unintentionally) selective glass that keeps outside mobile comms frequencies out and have indoor antennas that have strong and clean signals, but this is hardly the case for residential buildings.