I'm going to side with Hassat Hunter on this one. It's not a great idea to force the customer to install an extra 20 GB of stuff which is only there for the Classic edition and is not applicable to the DE.
Because it was not a fresh install, but an update, I got screwed over for a while because in the year+ since I first installed the DOS 2 alpha, the HD I was using had filled up, and I couldn't actually get the DE to work and could not figure out why until I checked and realized it wasn't on the drive I had thought it was.
I also couldn't tell Steam to just shift my DOS 2 installation to a drive with more space because "Can't move the game, an update is required". I had to delete other stuff to first free up enough space.