That isn't entirely true. The audio chat won't work in IE10, and IE10 support isn't a priority, but most everything else will probably work: https://togetherjs.com/docs/#browser-support

Edit: Ok, looking at the issues tracker, it looks like the current IE bugs basically break togetherjs on IE10. As such, hopefully this issue gets some attention: https://github.com/mozilla/togetherjs/issues/812