Google have posted a refresher on site targeting. For convenience here it is: Site Targeting Refresher
I don't think that it was the sole purpose. There is still alot of confusion amongst Webmaster exactly how site targetting works and effects publishers. As for the Ford Explorer ads not being contextual, I think most people don't see the wider picture. Sometimes contextual becomes to narrowly focused. I would definitely not mind to have a broader advertising base that is in some way related to my site. For example: If you have a site with content about computer games it might be very useful to have advertising about consoles, LCD's etc. showing up as well.