I made a "test page" that is simpler than that huge svg map: http://www.mrspeaker.net/dev/jq/testsvg.xhtml
It certainly looks like getElementsByClassName doesn't work - class selectors return 0 length. But even if they did work, the CSS stuff seems even weirder: opacity works (perhaps because it's a "normal" definition) but to get colours to work via JS I had to use the setAttributeNS method.
Anyhoo, I just thought I'd post that up in case it could help.
P.S. If there are serious changes need (or wanted) to get SVG stuff to play nice, I'd have a chat to Dmitry Baranovskiy (http://dmitry.baranovskiy.com/) - the SVG/JS master!