We used to get the F1 races uninterrupted on free-to-air TV, but now only the highlights are free-to-air. Even so, they only take a break about once every 15 minutes. Soccer and rugby matches, and hurling here in Ireland, are shown with only commercials at the start and end of half time (and before and after the match). Of course, NASCAR is a much longer event, but I'm still not used to the US levels of advertising. American football is another lengthier sport, and its many stoppages in play lend themselves to commercial breaks.
The extra breaks are also noticeable in other US shows when they're shown here. I was watching 'Medical Detectives' last night, and there must be at least three places where US viewers would've gone to a break in a half hour show. Over here, a half hour show typically only has a single break.