i think one thing to take into account is something similar to the bystander effect. when you donate to one person, it's easy to imagine that your money is directly benefiting them. when you're asked to donate to multiple people (whether it be 2 or 29k), you start getting overwhelmed and perceive your donation as insignificant.

i distrust market target marketing as much as the next guy, but why not put this data to use: why not market all of starving africa as one emotional story about a single individual. and then disperse that money however. ya know, throw some fine print at the bottom of the advertisement and call it a business model....