People in third-world countries don't care about the average U.S. site, and if they did, they would find someone with a computer that probably is 5-7 years old, possibly older, therefore they wouldn't be using that resolution.
What will be important, if you do care about them, is speed of load. Unless you are using GWT or other server-side user-agent sniffing to determine what to produce, then unless you have a mobile version of the site that the user probably won't use, then they will more likely than not be slowed down by your CSS3 and Javascript crap, that is- if you really give a shit.
Trying to provide usable news sites, etc. in the remote chance that you are the BBC is one thing, but 99.999999% of the time no one will care that your site looks good on a Nokia X2-01 and similar. They probably will care if it uses Flash and they can't view it on an iPad, or if it uses Java, or if it renders poorly, is hard to navigate, or is just too slow.
Most shouldn't obsess over low resolutions like that, and shouldn't use GWT or other methods of server-side user-agent sniffing to render content. And your CSS3 isn't going to jive with a Nokia X2-01 and the like, so don't even try that.