Don't be evil? Google's mobile services in Africa.

A recent article in The Economist discusses several mobile services in Africa, including Google Trader, "a text-based system that matches buyers and sellers of agricultural produce and commodities [in Uganda]. Sellers send a message to say where they are and what they have to offer, which will be available to potential buyers within 30km for seven days... These services cost 110 shillings ($0.05) a time, the same as a standard text message, except for Google Trader, which costs double that. In their first five weeks the services received a total of more than 1m queries." [http://www.economist.com/specialreports/displaystory.cfm?story_id=14483848]

So it sounds like Google charges twice as much as its competitors.. just wondering why...