Matt's made me look at the code *gasp* of the DotNetJunkies site. Here's the javascript check for browser type.

 if(csUserAgent.indexOf("Opera") > -1)
  return 0;
 else if(csUserAgent.indexOf("MSIE 4") > -1 && csPlatform != "MacPPC")
  return 1;
 else if(csUserAgent.indexOf("MSIE 5") > -1)
  return 2;
 else if(csUserAgent.indexOf("MSIE 6") > -1)
  return 5;
 else if(csAppName == "Netscape")
 {
  if(csVendor == "Netscape6")
   return 4;
  else if(parseFloat(csAppVer) >= 4 && parseFloat(csAppVer) < 5)
   return 3;
  else
   return 0;
 }
 else
  return 0;


The bottom line is that they're checking UserAgent, not object model, and don't bother with Mozilla. Moz pumps out a zero, and that translates to...

if(csBrowserType == 0)
 document.write(csIncludeDir + "/" + csFallBackFile);

when what Moz "deserves" is...

else if(csBrowserType == 4)
 document.write(csIncludeDir + "/" + csNN6File);

[update: And now for the final test -- I've emailed them; let's see if they make a change!]