While a sloop always has two sails, a cat-rigged boat generally has only one. Note that the mast is positioned very far forward, almost at the bow, making room for a very long-footed mainsail.
People have described Guild Wars 2 as a possible World of Warcraft killer, and while I think the two games are different enough to make this a non-issue, bringing the game to Mac is almost certainly a shot fired across thebowat Blizzard.