Navigon is great.... I love it way more then Nokia Drive.
I have tried to use Nokia Drive but in my area it directs me to the wrong place way to often.
However I understand in other parts of the world that it works really great. SO here is the news that I've heard about Nokia Drive.
It CAN be licence to all WP handsets if the OEM of the handset is willing to license it from Nokia. Nokia will retain Nokia Drive +.
So why hasn't HTC done this? Because they have there own GPS software that they want you to buy. However this doesn't mean they won't license it from Nokia (they haven't officially said they wouldn't).
In addition to this I believe Nokia isn't ready to release the Nokia Drive app to other handsets OEM's, even if they wanted it. Supposedly more to come in the New Year.