We have a better health care system, and are able to keep patients quarantined while tests are run to determine if they do have Ebola (if they have the travel history to suggest such testing is worthwhile). In the hospital, we practice good infection control measures.
An even more important factor is that we do not have the customs that they have in Africa.
That's right. The USA has 128 Million people who commute to work every day. Only 75% of these people drive alone. The rest really "commute", sharing the ride by carpooling, bus, train, subway, plane. Lots of filthy people contact all along the way.
Most of those people interact with others a couple of times each day at fast food joints, convenience stores, gas stations, dry cleaners, grocery stores, big box stores, etc., exchanging money, credit cards, products, etc., hand to hand.
Probably half of these working people have at least one meeting each day, crammed into little meeting rooms.
There are also 200 Million people who don't go to work, but interact with other people daily at schools, daycares, stores, bars, on the street, sporting events, etc.
People in the USA are just as filthy and stupid as people in the worst cultural conditions in Africa, just in different ways.
When ebola starts spreading in the USA, it will travel faster and farther than in Africa. Aiding in its spread will be the people saying, "there's nothing to worry about here," to their last gurgling gasp.
There are many ways in which our culture is not conducive to the spread of a disease like Ebola.
The most important way is in the way we treat the dead. We don't wash the bodies, we don't give them enemas. Instead, we ship them off to a mortuary to prepare for burial or cremation. During the funeral, most people do not touch the body. This is very different than the African burial customs which are completely responsible for the early spread of Ebola. Later on, nocosomial infection became important.
For another thing, even in the most crowded situations, we avoid touching each other. I noticed this at Disneyworld over the summer: no matter how crowded an area was, every American had a no-touch zone around him or herself. This was not true of some of the foreigners, who did not seem to mind bumping or being bumped.
Ebola requires direct contact to spread. While other potential means of spread have been mentioned--droplet transmission, fomites--there is no real evidence supporting those means. People who are sick enough with Ebola to be shedding virus in fluids aren't going to be out riding buses and so forth--they are really, really sick. I could see such a person hunkering down in their home until they die, but not being out and about contaminating public restrooms with their diarrhea and vomit.
If Ebola were easy to catch, this thing would have already gone around the world. Compare to influenza--it is about to sweep the northern hemisphere again, and it will essentially hit every continent at once, because it spreads easily and it spreads through aerosols. Ebola, on the other hand, is still confined to three countries--the imported outbreak in Nigeria is controlled, and I don't think there are new cases.