I'm finding that slipstreaming is definitely huge in this type of racing. One probably wouldn't be successful without it. I'm also finding, however, that even if you don't have someone right in front of you, you can also catch up by taking better/quicker lines than the other fellow through the turns.
Since NASCAR drivers are grouped into teams, there also appears to be quite a bit of teamwork that occurs between them as well. Teammates will draft with eachother to go faster, block for teammates, etc. The margin of error when it comes to wrecking appears to be greater as well. When you're in a pack of cars taking a turn after a straightaway, you really have to concentrate and be aware of those around you. One wrong nudge or bump and it's off into the wall or grass you go.
Don't get me wrong--I absolutely LOVE road racing such as touring cars, GT, etc. and NASCAR is definitely a different type of racing, an aquired taste perhaps. But the more I try to discover what the appeal is, the more I begin to understand what the appeal is.
Not sure about Marcus Ambrose. Good question though.