jQuery - scrollTo

On page 76 of my edition of the jQuery: Novice to Ninja book, there is a discussion of scrolling. The point is made that, if a page uses quirks mode, then the $(“html”) selector will fail. The alternatives given are using $(“body”), or “just to be sure,” $(“html, body”). The book then goes on to explain that using both will not work properly in Safari, which is why the book then goes on to introduce the scrollTo plugin.

This is one of the few areas where this otherwise great book is vague. Why not just use the $(“body”) selector? Are there drawbacks (possibly browser-specific) to such an approach? If it works, it seems to me that is better than adding in another plugin. I understand that the plugin in has some other great features and the authors wanted to introduce it, but (in my opinion) they rushed the introduction a bit.