In quotations because different folks seem to have different ideas regarding the definition of the term "Digital Art". There are quite a few debates raging amidst artists regarding the validity, legitimacy, authenticity, or something or another of this comparatively new format.
The thing is, this comparatively new format is not very well defined. Computers do two thing exceptionally well. Store & retrieve data. And compute. This is usually utilized in two major ways. First, to make, and maintain a list of numbers. Second, to run mathematical formulas using numbers. That's all a computer does. Really. When this list of numbers is sent to the video processor, it generates pixels based on the numbers to produce an image. If the same exact numbers were sent to an audio processor, it would create a sound.
In essence, an image, any image you see on a digital display device (computer/laptop screen, cellphone display, handheld videogame consoles, ebook readers, iPod, HUD enabled Contacts, etc.) is a list of numbers. It could be a photo. It could be a cartoon. It could be state of the art polygonal "3D" graphics. It could be a still image. It could even be a video, which is essentially a collection of still images. And the only way to manipulate and/or modify these lists of numbers is to run them through mathematical formulas.
This, in essence is digital art. A series of formulas to modify a list of numbers.
The problem is different programs try to cater to different groups of artists from different backgrounds. So programs like Photoshop & Painter use easy to understand names like "Canvas" & "Paint Brush", instead of "List of Numbers" & "Mathematical Formulas to Modify the List of Numbers Based On A Given Set of Variable". A traditional painter sees a name like "Paint Brush" and automatically expects the mathematical formulas to act like a real paint brush, which it doesn't. So you end up with a traditional painter complaining about how/why the "Paint Brush" of a given program doesn't quite stand up to the expectations of the painter.
The digital medium, in an attempt to be more intuitive & user friendly end up unintentionally misleading the people it's trying to cater to. The people trying to work with these programs, in turn, end up comparing lists of numbers to the physics & chemistry of the intricacies of pigmented fluids and it's interaction with processed cellulose & gravity. It's like comparing apples to jellyfish. With one side arguing the apple to be superior because you can't just bite into a fresh jellyfish, while the other side argues the apple lacks bio-luminescence.
Care to guess what any 2D/3D Animation Software does? Lists & formulas. Video Editing? Lists & formulas. Your web browser? Lists & formulas.
At the end of the day it is just a medium. Like ink & paper. Like the newspaper on the table in front of me, or an issue of Action Comics #1. What sets today's newspaper, a hundred dollar bill, or a the first issue of Action Comics apart from one another isn't so much the limitations & advantages of processed cellulose & pigments, but what their respective producers decided to do with the medium.
The exact same principle applies to lists of numbers & mathematical formulas used to manipulate them.