For many many sites it really doesn't matter if they don't support 3rd world countries - what value do we gain from working hard to support people with no money to spend? Advertisers aren't interested in them, we can't sell anything to them. It sounds selfish but society is based on exactly that way of thinking.
Opera Mini is also relatively unique in having great text-reflow which is an important feature for people with bad eyesight, even in rich countries.
Opera Mobile also has great text-reflow, which makes it much more usable than other mobile browsers in my mind.
The approach taken by other mobile browsers for desktop websites often yield pretty bad results, and some sites (such as hackernews) are consistently broken.