It appears that inside a mousewheel event handler, wheelDelta is not added as a property to the jQuery event object anymore, because mousewheel is not in the list of events that have mouseHooks added. Only some of the following events do, namely the ones that pass rmouseEvent of the following:

"blur focus focusin focusout load resize scroll unload click dblclick " +
"mousedown mouseup mousemove mouseover mouseout mouseenter mouseleave " +
"change select submit keydown keypress keyup error contextmenu"

This renders the wheelDelta property in mouseHooks useless, since no other event passes this property. Only mousewheel provides this data, but it is not used by jQuery because it's not in the above list.

It would perhaps be a better idea to either drop wheelDelta from mouseHooks or support mousewheel as an event like the other mouse events above.

http://jsfiddle.net/3cB95/

(Of course, e.originalEvent.wheelDelta works; my point is that wheelDelta is never used although it is in mouseHooks.)