It's kind of sad that Africa is no longer served by US carriers. In the post-Pan Am era, TWA and Delta used to fly to Cairo; the former went out of business and the latter dropped the route after September 11th.
Fortunately, Continental's Accra service will change this.
There was a very short-lived venture, USAfrica, with World Airways MD
-11s from Dulles to Johannesburg.
Years ago, United had discussed serving Johannesburg by way of São Paulo. But there's absolutely no hope of that service at this point.
My guess is that African services COULD be profitable, but long-range aircraft are MORE profitable on European, Asian, and South American services.
British Airways, Air France/KLM, and Lufthansa/Swiss have extensive African networks, so the alliances have their bases covered. The trip isn't easy from North America but the connections exist.
I think the only chance that another US carrier would serve an African destination would be from a European hub, analagous to the India flights. Delta could fly from CDG
or Northwest from AMS
. But regulatory issues are a nightmare and the revenue might be insufficient. But we'll see how Continental does in Ghana...