If anyone has tried going to
www.keyhole.com you can see that Keyhole doesn't exist anymore.
Google Earth isn't just a cobranded version of Keyhole. Google had owned Keyhole for a long time (2004, October), but now releases it under its own brand, instead of the Keyhole name.
The transition comes with a few changes, the most notable, no charge. However, the program is THE SAME THING, so I see no sense to comparisions between the two names for the same thing.