A cursory look found this. I have no idea if it's applicable. Are you declaring it on the very first line without any spaces or other characters before it?
I had a mission to make everything I did better than my predecessor(s), who didn't seem to bother with things like Validators. Not that it's the Almighty Lord of 3W's, but ...
From the W3C website. They also list other ways of declaring the character encoding depending on the doctype.
It doesn't surprise me in the least though if IE10 simply isn't up to snuff on standards. It's IE, after all.
Yeah; it's just as I mentioned above, editing all those templates for something fairly "trivial" ...
And hope that IE10 recognises the MIME type (one of the things I suspect throttled XHTML uptake in the first place).
Indeed, you are wise; even the GoogleMonster got in on the action.
So sad to sit by and watch "standards" leave your work in the dust of time ...