Jeff 

It's a misconception I see frequently that the DNN url rewriting just does rewriting (not saying you have this misconception, but others certainly have).   A DNN Url Rewriter / Friendly Url Provider generates the friendly Url and re-interprets them.  If you use the example of a modem (modulator-demodulator) you could say the DNN Component is a FriendGenRewriter.  Or something.

By installing an ISAPI rewriter you will indeed be able to make DNN interpret whatever format you like (as long as you can somehow encapsulate the tab Id) but the problem is getting DNN to generate the friendly Urls in the first place  Sure you can post them into the Html wherever you like but 90% of DNN links are generated by the code itself, so in my mind any type of ISAPI rewriter isn't going to work that well, unless it is reformatting the code on the way out as well as on the way in, the way the Inventua Href exchanger works (from my understanding, it scans code and replaces Url tokens as it is emitted from the server, and rewrites when the code comes back in again).

A 'proper' Url Rerwriter/ Friendly Url Provide for DNN integrates in with the Core DNN code, and lets third party modules and other code generate the correct 'Friendly' Url within the DNN code itself, removing the need for secondary processing on the Html.