What a cool write up to go with the launch - Canon should have him help all of their launches. The photos are incredible and his humor and honesty left me amused and impressed. I have been running the numbers in my head all day - what gear can I sell, how much can I put on my AMEX, etc., for this lens. Alas, I need to get A LOT more paying work before I can afford it.
As for the 100-400 comparison, it is an unfortunate reality that the cost between the great and greatest are so high and the differences so small in relation. This is true of all fine things, though, whether it's cars, watches, amplifiers/speakers, etc. I am sure the build quality is significantly higher, though. In my own experience, I couldn't believe how much better the build of the 70-200 f/2.8 IS II is over my 70-200 f4 IS - made me realize that there was more to the extra cost than just a tripod mount and an extra stop. I'm sure the same will be true of the 200-400.