Wee! I get to deal with support to find out why! I can't really think of anything short of being hacked, which seems unlikely since I changed my password recently to something crazy and 20 characters long (keepass), there have been no hits on Steam Guard since my last loging like someone was trying to get in, doesn't look like anyone has accessed the account for a month which seems about right for the last time I tried it, and there can't be any fraudulent purchases because I don't purchase anything from them.
So it'll be fun to find out the reason and hopefully get everything back. Because you know, Steam is awesome and shit.