Safari recently shipped the level 4 version of :not(), which allows complex selectors for arguments, putting it on par with jQuery’s hitherto non-standard implementation. See the release notes. The current incarnation of :not() only allows a single simple selector for an argument, so a complex selector like p div will not work in today’s browsers by design.
A complex selector is an expression consisting of one or more compound selectors separated by combinators such as descendant, >, ~ and +. A compound selector is a sequence of one or more simple selectors. div is a compound selector consisting of one simple selector, and p div is a complex selector consisting of two compound selectors (each of which consists of one simple selector), separated by a descendant combinator.
It is currently not known when this will land in the other browsers, though it’s unlikely the new specification of :not() will change at this point — the current level 4 definition is a no-brainer and if the original WebKit strain is daring enough to implement it, then it’s really only a matter of time before it makes its way into the other strains (including Blink).
After almost five grueling years of waiting since the FPWD, we might actually finally get to see a CR of selectors-4 real soon. Consider me pumped.