Velocity in resource files fails to render

Some resource files under contains velocity but velocity does not render and causes problems. For example,

../webapp/resources/js/xwiki/table/tablefilterNsort.js

Visit http://localhost:8080/xwiki/resources/js/xwiki/table/tablefilterNsort.js

Get:
var image_path="";var image_up="$xwiki.getSkinFile('js/xwiki/table/img/arrow-up.gif')";var image_down="$xwiki.getSkinFile('js/xwiki/table/img/arrow-down.gif')"
...

See broken images in the table sorter example:
http://extensions.xwiki.org/xwiki/bin/view/Extension/Table+Sorter