Just so I'm not missing something, are there browsers which would support the Webkit CSS but not support DOM manipulation? Or are you concerned with people running NoScript style plugins?
Yes, NoScript is a problem. However, I was referring to other scenarios in general where a problem can be solved by just adding a <div> in HTML code. It seems more economical to me to add the <div> manually to the HTML code as in this Webkit example rather than writing a JavaScript routine to manipulate the HTML code at runtime on the client's machine as you suggested.
Not being hostile, just want to clarify.