What's the biggest thing to happen in OW in the last number of years? It's clearly Danica (rightly or wrongly). Her car has a Honda engine in it. I think you can see where I'm going with this.
Continued press/hype give Honda a very compelling reason to stay. This year's Indy ratings are much hyped, but they were really Danica ratings, not a sudden fundimental change of heart by the public.
As for why is all this stuff/2007 important? We've seen the situation before, it could potentially kill the series! I personally find it an interesting situation.
Watching the race and seeing the monster crowd at Kansas had me thinking about this stuff. I think what really hurt CART was the negative perception that the series wasn't worth anything due to names leaving. If the manufacturers left would a similar perception swing occur? I don't know that it would. I don't think such a fall would be preceived so negatively because of the IRL's legacy of not always being as glamourous and the fact that it wouldn't be falling from the one time status as a major league sport.