The innovator-iterator argument seems to be a red herring. The real issue here is building bullshit apps vs. helpful apps. I think focusing on making helpful apps is a more important message to developers than trying to "fix poverty in Africa" which is a nice goal but not something any web developer is likely going to impact.

The reality is no one is going to come up with an idea like mFarm without REALLY understanding that audience. You won't understand an entire ecosystem just by sitting on the corner. If you want to help Kenyans, instead find some promising Kenyan entrepreneurs and offer to be their code monkey, review their code or host their website. I think humility is crucial if you want to contribute to a market you don't fully understand.