Most of the first world, at any rate, has faster internet (and a greater percentage of people with broadband) than the US.
I would guess two billion of the worlds people are in places with crappy internet. Africa has cables around most of the coast, but interior areas often rely on satellite. In China, everything has to slowly grind through the great firewall before it gets to you…same thing in Ethiopia, where a state monopoly owns access. In rural South Africa, people use cell phone modem that frequently times out due to overcrowding. In rural South America, it’s all slow satellites.
While these areas may constitute a limited (but growing) number of internet users, I think many content providers are uncomfortable producing knowledge and discussion that is only useful to the world’a rich.
“Many”, perhaps, in absolute terms, but web designers who care about that are a small minority nowadays. Have you actually used dial-up Internet in the past few years? I have. Almost no web sites are designed to accommodate slow speeds any more. Most of them just assume that everyone has broadband, and that they can therefore get away with being wasteful of bandwidth.