Pretty self explanatory. The -webkit-grab and -webkit-grabbing cursors seem to only work on Macs, verifiable using the URL provided: http://trac.webkit.org/export/37902/trunk/WebCore/manual-tests/cursor.html
Even worse, the following CSS will produce a "pointer" cursor on Windows! .grab { cursor: url(grab.gif), move; cursor: -webkit-grab; } Not good!
Confirmed in both Chrome and Safari on Win7. The default cursor doesn't change.