It's true that there is a vast resource of racing talent in the USA, but for most, the path to racing glory is via oval racing, namely IRL or NASCAR. But most professional drivers are well aware that getting into Formula One is difficult, and retaining a seat is a crapshoot. For instance, Jeff Gordon is a fine example. He even did a promo drive in a Williams, and rumor is that for a short instant, the door was open if he wanted to go that route. But what is the expected income for a Formula One driver? Even a very good driver pulling in 10 million has a career no more than ten years. Jeff Gordon has been a big dog in NASCAR since 1993 and he's been making a truckload of money. His income for 2009 was estimated 23.4 million. Dale Jr made 27 million. So there's no obvious reason for him to attempt Formula One. And there's a lot of drivers in his circumstance, where the income over a very long NASCAR (or IRL) career adds up to a large amount of money.
Some make the assumption that Formula One is superior to every other series. I respectfully disagree, because I believe that it's a case of specialization. I've seen oval racers fail at road racing, and I've seen road race specialists flounder at ovals. In fact, some former Formula One prospects are now earning a living in NASCAR or IRL. For instance, Takuma Sato, Narain Karthikeyan, Nelson Piquet, Jr., Christian Fittipaldi, Jacques Villeneuve, and Juan Pablo Montoya to name a few.
Racing has become so specialized and competitive that a driver can prosper at one form of oval racing, yet fail at another type of oval racing. Steve Kinser is a good example, he owned dirt oval racing, yet failed at a NASCAR career.
The career path an athlete can follow is largely dependant on the immediate environment and local support for that athletic endeavor. If Peter Crouch had grown up in the USA, he most likely would be playing basketball in the NBA, and if Jeff Gordon had grown up in Europe, he most likely would have wound up a Formula One star.
And of course, we have the pay drivers, where talent takes a back seat to connections and sponsors. That's a whole different kettle of fish.
But I watch IRL and NASCAR a lot, and see a lot of very talented drivers. If but for a different career path, many of them could have made it in Formula One. My wish would be to see Kyle Busch in Formula One, now that would shake things up a bit.
But sometimes, a driver's final destination may not be as when it first started. take the example of Tomas Scheckter, son of Jody. His racing career was similar to many, karts, then Formula Vee, Formula Fords, Formula Vauxhall Junior, Formula Opel Euroseries, Formula 3, Marlboro Masters F3, FIA Formula 3000, and Open Telefonica by Nissan before going F1.
Scheckter was signed as a test/reserve driver by Jaguar for the 2001 Formula One season, but was soon fired after being charged with soliciting a prostitute. He now competes in IRL. oops, we didn't see that one coming.

Racing should be decided on the track, not the court room.