van I think that all depends on preference though I do agree to some extent. While modeling massive terrains or whole terrains would be very taxing on any engine and that using heightmaps would help optimize the game play, modeling bits and pieces of the terrain has it's benefits. such as:
over hangs, caves and other small player important terrain objects.
I think that a person should have knowledge using heightmaps as well as modeling when creating their terrain. You would be a fool to think you can create every little detail you wanted from a simple heightmap. though as some of the programs get better then things will change but as it stands now you should have experience with both methods.
Cheers,
Dave