I beg to differ. Their monopoly can't be broken on price alone. Let's take an example. Someone in the United Kingdom is sending £100 to his relatives in Kenya. Western Union normally charges a commission of 15% (i.e £15). Now a new service provider comes in to existence, and it charges only a commission of 5%. But still people will continue to use WU, as they are unwilling to use a new service provider.
Maybe? People do love to follow a pattern? I don't know how they operate in Africa, but maybe WU and MG have convenient locations and that helps them own the market? My hope is that one brave African learns to use BTC and his friends see the benefit. I think we are going to find out in the next few years.