Ok, the way I see it is true XHTML is what ever is going to validate under the Strictest Rules of XHTML.

That's a fair meter.

Now, if only you had tested what we were talking about.
<p>This is wrong<br><br/></p>
should be
<p>This is wrong<br></br>...or not</p>

Once you do that, you'll get "This document was successfully checked as XHTML 1.0 Strict!". So, both <br/> and <br></br> are accepted by w3c's XHTML validator.