I think the key is "third-world countries," those that don't have the resources to have collections of books, supplies, knowledge, or the ability to keep any of that up to date. The OLPC removes the need for the givens in first-world education systems, and assuming their other basic needs are met, provides a window to possibilities they've simply never considered.
For first-world countries, I don't think the software/interface is quite there yet for replacing traditional school work, but it's getting closer by the day.