lucy24 - 10:30 pm on Mar 27, 2012 (gmt 0)
Google doesn't just need to render your page to provide the preview image
Preview is irrelevant to this discussion, because Google Preview is not a robot and is not affected by robots.txt.
If you are hiding CSS/JS from search engines, you probably have something to hide.
Would you like to look at my piwik.js file and see what black-hat evils I'm hiding? Be my guest. For obvious reasons it isn't blocked to humans-- and so far it isn't blocked to empty referers, though possibly that's what I should be doing.