I've got to agree with this 110% regarding the U.S. I've ridden and shown my whole life, on a national and international level. By luck of the draw, my parents aren't billionaires and so working for all my trainers was the reality. What did that get me? A great appreciation for the sport, some awesome opportunities and a cold slap to the face when I aged out of the juniors and no one wanted an adult rider. While I still ride, $100,000k and up horses (or .5 mil and up for olympic level) just aren't a possibility. So yes, 99% of riders from the U.S. are loaded and the other 1% got a miracle sponsor behind them.
Now, the riders from South America are quite different. In the U.S. sponsors are a dime a dozen ONCE you've proven yourself at the top level. Companies fight to sponsor a good international rider. My boyfriend, who ironically goes to Argentina to buy his young jumpers at a fraction of the ones for sale in the U.S.) is Venezuelan-a country very much in support of it's riding team (at least in all ways but financially!) We've spoken to the federation about it as the bf is very well qualified (thankfully to a very generous sponsor!) and they will not consider a spot on the team without a huge "donation" by rider or sponsor. Payment to be on the Olympic team!?
As far as Argentina-an Argentinean rider here in the U.S. actually qualified the country as an individual-yet the federation's prez has a son who rides, ergo that is Argentina's representative. Not the guy who qualified the country, but the kid who had a connection. With corruption like that-can you blame talented athletes for being deterred from wanting to try to represent their country. Money rules 99%, corruption/name-dropping rules the rest.
I still have faith in the Olympics and love watching it. Hell, hopefully I'll be in Rio 2016 to watch Venezuela....if we can cough up enough $$ before then to pay off the federation.