Don't get your logic here?
I used to use the car sat nav, google and my truck map to plan my route, very rarely asked anyone directions for the reason you give.
The proposed ban would mean me having to buy a HGV one, when all I use it for its the final mile or so to the destination instead of the old A-Z's, after all its bloody hard to navigate a 44 tonner in central London as it is without trying to find the exact road on the A-Z when there are 6 roads in an inch on the map, much better to see exactly on the sat nav. Add to that most HGV ones do one of 2 things if they think the route is not possible (7.5t limit ect) they either plan no route or revert to car mode.
I trialed a snooper one on my current job (a lot of London track access points are in 7.5t built up areas) and it was no better than my original Tom Tom car one, once the destination is inside a restriction it cannot cope and comes back as not possible. This is where good old fashioned common sense comes in and a quick look on google at the destination usually helps.