I thought the same thing. So, I contacted the MS representative on the uPNP.org site, and sent him a capture from my DNS-321. It turns out that DLink is not properly supporting uPNP at all. It's abysmal. Their uPNP.org rep does not even respond to e-mails. Microsoft's representative (Toby Nixon) forwarded my Wireshark capture to the Windows Media team who confirmed that the responses from the DNS uPNP server were not correct.
The way to correct this in DLinks absence is to install funplug and Mediatomb which works pretty well.
TheWitness