Well, I am presently in a country that is near at the bottom of the chart in both of speed and cost, and I can assure you that it is not scaled according to average income (a fraction of UK average).
To give you an idea of how expensive it is, the "top of the range" 20Mbit/4Mbit (with a line stability ranging from "passable" to "over 40% packet loss level of usable") would cost 244 pound per month. 33.50 pound get you the basic 1MBit/724Kbit package.
Mind you, I am not saying that cost of labour has no impact at all, I think that it might play a big role in countries with relatively mature net infrastructure (regardless of whether the country is classed as developed or developing), but outside that, it is a different story.