It's just a tool or a medium. Painting with oils and painting with acrylics is still painting; just like drawing with a tablet is still drawing. Digital art is just regular art done in a digital medium.
It is meant to exist on a digital plane or created digitally. But there's a lot of blurry spots as I'm sure you know, things that were digitally enhanced or finished or digital models printed out in plastic with a 3D printer.
True digital art to me is an artform which cannot exist without computer technology. Vector art can be done manually, sculpting: same thing. Computer generated images (fractals) such as this one is true digital art. [link] No human can reproduce this amount of detail manually (and not be bored in the process...)
For one it consists of pixels as opposed to clay or oil paints, etc... And until you print it, you don't actually have a physical copy of your artwork, it only exists in virtual world, I mean computer screen, excuse me
Well, the first thing that comes to my mind is "clean". Digital art generally looks cleaner than traditional. You can achieve the clean look with every medium of course, and you can make a 100% digital picture really messy. But to make a traditional painting look clean, you still have to get your hands dirty, and making a messy digital picture requires no dirty hands at all. So this is my association. It's more because of the method, less because of the result.