There are 3 or 4 drivers that have dominated the US/Canadian on road scene over the past few years on a consistent basis. Paul Lemieux, Rick Hohwart, Kevin Hebert and most recently Andrew Hardman.
I was brought up racing with Paul in Milwaukee. Trackside Hobbies, a carpet track was the only place we had to race. There are no on road asphalt tracks at all in S.E. Wisconsin and to find one you have to travel at least 2 hours south to Joliet, IL (Leisure Hours) to practice or race.
I now live in So Cal so I have the opportunity to race with Rick. The problem that all of these guys currently face is that there are simply no tracks for them to practice or race on a regular basis. The closest track for Rick to run on is over a 100 miles north in Camarillo, CA. It's open two weekends a month. He also has an occasional opportunity to run at the Tamiya USA track (which is open only to Tamiya Brand cars) 2 or 3 times a year when the track is open to all brands of cars to run at a club race (Speedtech Gran Prix). Recently a very small on road track, CAL Raceway, has been restored but it is way too small to get any meaningful modified practice at.
I'm not sure about the racing scene in the Toronto area where Kevin and Andrew live, but since Fast Cats closed (a carpet track), I'm sure both of them are left with little opportunities to race/practice on a regular basis without a significant distance to travel. That's not to mention the very short outdoor racing season these guys have in Canada, if there was a permanent track for them to race at.
What this all boils down to is that these guy's only real opportunity to race is at the large events themselves. I am amazed at how well they perform with so little opportunity to practice... on asphalt or carpet. Their finishing positions at the IFMAR World's were incredible considering the small amount of wheel time each had to prepare for this event or any event for that matter compared to their European and Asian competitors.
Lastly but probably most important is the fact that with the exception of Andrew (who turned 16 last weekend) there is no up and coming young talent that is being groomed to eventually replace our veteran drivers. They're all running off road. With the very high operating costs to run a good track these days severely limiting the number of tracks that exist in the US and the popularity of off road in North America attracting all of the young talent, I'm afraid we won't be competitive on a world scale in on road racing for a long time.