With 39% of all boxes still running XP, I'd hope that XP would still be supported.
It worked fine with 18.104.22.168 - and it wouldn't make much sense to use operating system specific calls that might limit their market.
I'd move in a heartbeat, but it's would take a whole lot of hours to get it all set up again.
Sadly, on my main development box where I'm typing this (I develop database software), I'm running lowly XP (and I own several Win7 dual Xeon screamer boxes). Would take way too much downtime to move. Ahhh!