What they have is the ease-of-installation. What it lacks is integration into a wide, multifunction web site. And that would be the utility of being able to reproduce the functionality within Drupal -- a more integrated solution in the end.
I don't think the goal should be to make it as easy as it is on ning.com, but it could certainly be easier than it is now. One huge thing would be to make it significantly easier to create an installation profile. I think the whole installation profile thing is underutilized because it is such a pain to create and maintain one. Will that be improving in Drupal 6?
The ease of setting up more networks or "sites" on ning is something attractive. Yeah I guess an expert can make a ning-like site using drupal with quite a few modules. But then again, that's not what drupal is all about.
It's so easy to change the look of the site and no need to go into the File Manager and change things from there. Also appreciate the ease of inviting friends by importing the address book from popular emails.