I have video of that MLK (I watched it live on TV actually, his teamate had done the same arial stuff I think a couple days earler, they pulled the 3rd car from the race immediately after the 2nd car flew) and a porshe that did the same thing...not quite as much hang time on the porshe but still the same thing. I heard something about certian places of some tracks being redesigned to keep the chance of "flying" down a bit. I guess no crests(or hills or whatever they are called) on straightaways, however small they may have been.
What year did that merc fly anyway?
edit: just did a quick google, here's the merc vid
http://www.funvids.net/videos/Play.asp?Video_ID=113