This may be irrelevant to original comment but does querySelector work in all modern browsers? My understanding was that it doesn't and so there is need for CSS selector engines like jQuery's sizzle.
The page implies that there is limitations to the IE8 implementation, and that it's only available in relatively recent browsers. In addition, I believe that sizzle implements a set of selectors larger than most or all browsers support natively, although this I am less sure of; the Sizzle documentation certainly implies it strongly:
