Just had a look to see if I could find some more reliable statistics. Frustrating. Within a short time-frame, I couldn't find what I was looking for for global computer ownership and usage. Mostly it was Yahoo answers (Swiftian Yahoos, perhaps?). I'd be interested if anyone could find a decent set of stats for this.
The average of what I saw seemed to be anywhere from 3-15% for global computer ownership, and 15ish% for computer access.
As a couple of posters said, it'll probably be mobile phone (or some other mobile device rather than PC) access that will be important for global ebook take-up. Another interesting question is what proportion of people in less-economically-developed nations have a mobile phone that was produced in the last five years. Anything earlier than that certainly won't be a 'Smartphone', or capable of being used as a reader.
It will be interesting to see whether ebooks make it to such countries on devices that are already owned by the populace (as a secondary function), or whether charities/NGOs will intervene to provide reader devices. I suppose it's likely to depend on which technologies become cheapest to develop most quickly. I don't think readers in these countries will be too troubled by the 'which type of screen is best to prevent eye-strain' debates we see on MR.