CSSResourceToDom questions

I'm working on including resources mentioned in css, and I've come across
the CSSResourceToDom method in CSSUtils. Can the author of this method help
me answer some questions?

1) Why is this method used in EmbeddedCSSResource, but not present in
HTTPCSSResource?
2) What are the distinct advantages of this approach vs. just using the text
data of the css to get the information we need for the tests?

Thanks!

Cheers,
Laura