On the ":checked Selector" page (http://api.jquery.com/checked-selector/), the description states:

"The :checked selector works for checkboxes, radio buttons, and select elements. For select elements only, use the :selected selector."

The :checked selector does not work on select elements. It works on the option children of select elements (see http://jsfiddle.net/jhfrench/mr7koj73/ for demonstration).

Suggest enumerating the destinction with this description:
"The :checked selector works for checkboxes, radio buttons, and "selected" options of select elements. For the selected options of select elements only, use the :selected selector."

I think it would also be a good idea to include a third example which illustrates using :checked with select/option elements.