I'm afraid you don't understand what Microsoft is asking...
Suppose you own a patent.
I violate your patent and you then go to sue me.
For you to even file a lawsuit, you have to demonstrate that you are indeed the patent holder.
Without this your suit will be tossed. You then make your claim of alleged patent infringement.
What Microsoft is asking for is that they want to argue that , while you were granted a patent, that the patent which was granted shouldn't have been granted in the first place, therefore they are innocent of violating your patent.
What this does is place the burden of proof on you to not only show that I infringed on your patent, but then to defend your rights to the patent in the first place. So as the plaintiff you now have the extra burden to defend your patent.
This makes it more expensive for you to sue anyone defending your IP.
It also means that its easier to defend against alleged patent violations.
Going back to your analogy...
It doesn't really work. It would be saying that you didn't really steal my car because I don't really own the car because I have a car loan. And even that fails.