The hope was that we could export a lot of knowledge in a very small package to people who were susceptible to its uptake. We might not see the benefits of OLPC until these children become adults.
One of the problems with providing charity in Africa is the ridiculous amount of superstition that pervades every aspect of African life. If we can remove one or two of these superstitions, then uplifting African society will be so much easier (perhaps it is ethnocentric of me to assume that African society wants and/or needs to be uplifted, maybe that's why the program failed?).
There was a video posted a while back where the students of a South African university were mad that they weren't learning about magic. Yes, magic. They had "seen magic" in their villages and were upset that the university was teaching them that magic wasn't possible (It didn't help that the lessons were coming from white people, but that's another issue).
You can't fix adults when they get all the way to university with those kinds of superstitions, you just need to start on the next generation and hope the lessons stick.