Where did "Top 5" come from. Here is the rule from the official website:
1.13: Any driver who made the A main in stock in the last 5 years at any of these national events, IIC, US Indoor Champs, Snowbirds, Carpet Nationals MAY NOT run in the 17.5 classes.
Perhaps they did not update the rules page for '09/'10 this is from the home page of the website, also changes wording to ROAR Nats, encompassing all genre
Class Restriction:
If you have finished in the Top 5 at a National level event (ROAR Nats, IIC, Indoor Champs, Snowbirds), you may not participate in the 17.5 class. For example, if you finished 3rd in stock foam sedan at the ROAR Nats, you can only run 10.5 Foam Sedan, 10.5 1/12 and 13.5 rubber for the Grand Slam.