Whether or not an operating system has a remote command shell says nothing about its ability to withstand other attacks such as denial of service attacks.
There is great customer interest in UPnP, especially as more UPnP-capable devices are becoming available. Folks who don't want UPnP can certainly turn off the service, but just applying the patch is sufficient to return it to safe operation.
The only thing that a Web site can do with this is read selected files from a users machine if they know the name of the file.
The real problem is Netscape Communicator taking a powerful script and putting it out on your computer in a locale where any Web site can find it out and run it.
We're recommending as a work-around that customers who are worried about this vulnerability disable active scripting, while we develop a patch for this.