The specification for xhtml-1.1 says that the server *should* send application/xml+xhtml in the HTTP header but that it *can* send text/html in order to remain backwards compatible with older user agents, IE for example. As long as the doctype is set correctly (and it is) it is still valid xhtml-1.1.
In fact, if you use the validator and let it auto detect the doctype it correctly detects xhtml-1.1 and validates the page using that specification (ignore the errors, I’m still workin’ on it). Browsers will also detect it, including IE, and use the correct specs to render the page. They also render the page in Standards Compliance Mode, including IE.
Trust me on this, I researched it *extensively* before making the jump to xhtml-1.1, I didn’t just blindly decide to change. I read the entire xhmtl-1.1 specification. I didn’t just skim it or skip any parts I read the entire thing. I read the XSLT-1.0 specification to make sure I was doing it right in the xsl. I also read TONS of threads from all over the world discussing this, including from IE support sites, apache, mozilla, w3c and web designer sites.
MS officially suggests using text/html in the HTTP header when serving xhtml-1.1 documents to IE. Mozilla, Opera, Firefox, Konqueror can all correctly use application/xml+xhtml and officially suggest that is what you send in the HTTP header but **ALL** of them are also backwards compatible with text/html.
None of the text browsers, as far as I know, can use application/xml+xhtml yet but, just like IE, they can correctly render an xhtml-1.1 page validly and in Standards Compliance Mode with text/html in the HTTP header.
So, to sum it up:
The site is validly serving XHTML-1.1 (except for the errors I haven’t fixed yet) that is recognized by all browsers and correctly rendered. The server doesn’t have to send application/xml+xhtml in the HTTP header in order for it to be valid, it can send text/html too.