RISUG isn't a cure-all. Transmission is still possible through microtears and directly through the skin of the glans penis and the meatus. And RISUG does nothing to prevent female->male transmission.
It's far too easy for "RISUG inactivates HIV in some components of semen" to transmute into "It's ok baby, I got a shot that protects me from HIV!"
How do men (heterosexuals) get infected then?
Also, HIV transmission is more likely with other STDs. If you have open syphlitic sores on your penis, you are more likely to contract HIV.
There's been some speculation about why rates of HIV vary so widely across Africa.
(http://www.irinnews.org/Report/91305/AFRICA-Risky-sex-does-n...)
Unsafe injection is the most efficient way to transmit the virus. It's scary that so many injections in the developing world are unsafe. (UNICEF say "16 billion injections are administered each year, of which 90 percent are for curative purposes; 50 percent of the total number of injections are unsafe.")
(http://www.irinnews.org/Report/85278/AFRICA-Poor-syringe-hyg...)
The amount of money needed to make a difference is probably (relatively) small. But changing behaviour is hard.
Assuming 1% of partners have AIDS and someone had 10 partners and 35 events per partner.
.01 * (1 - .98)^ 35 = 0.5% per partner. And 1- (1 - .005) ^ 10 = ~5% chance of an infection in a lifetime.
Or working the other way if the average person with aids has 35 'events' per partner and 2.1 partners after infection the infection rate will increase.
PS: Real models include differing M/F infection rates, stratification by age and other vectors like transfusions and IV drug use.