Google Chrome Comics
google.com
google.com
I had to laugh when I read the contrived comment of one character asking "why is this application downloading the entire Internet?" when looking at the Chrome task manager.
Uhh, no, it wouldn't, because chances are strong you'll screw something up. Whichever technology takes the current model and extends it gracefully but usefully will succeed in taking the web another step forward.
They're using the phrase "start from scratch" to explain their thought process, not what they actually built at the end of that process. And that's generally okay. You can use any method you want to figure out where you'd like to go, before you try to work out how to get there via small, continuous changes to the status quo.
I found the new JS vm the most interesting part, I bet Steve Y. had something to do with that. I can't wait to read what he'll write about Chrome. I bet he's very happy right now... in his pants! (Sorry couldn't resist.)