Not quite so. All route must be calculated. If you save a route it have distance on roads. If you see any point the navi show the rough distance by straight line.
New models of navi have more functionality than yours. When you choose the point they calculated lenght of route to it according your current preference. You can see it or in special data sheet or even on map. On some model like motonavi or Nuvi 3790 you have possibility to see all route for any route method simultaneously.