Oh, something I forgot, the texture, and tangibility of "real life" art, or the way that the way light plays off of the brush strokes on the canvas. I know there are programs/plugins that can mimic this effect, but it's a poor imitation.
That's why you have professional printing
Prints are great, but the texture of prints, whether matte or gloss, doesn't complement the art like the texture of paint on canvas, or may other media can do. And a one-off is better, or more personal in some cases, than something that's been printed off a thousand times.
I don't know if this is veering too off-topic, but the same applies to sculpture vs 3D modelling software. (Although technology does seem to be blurring the line here, aren't there machines that can digital 3D models to 3D sculpture?)
One final thing: Art theft. Yes, with traditional work, someone can copy your style, or your ideas, they could trace your work. But with digital work, you can do all that, do it easier, and so much more. >_< People can duplicate your work, claim it as their own, spread it all over the internet. Although that I guess is just a product of our technologies, and the time we live in. And I guess even studio work is not safe, if you upload photos/scans, people can always get their hands on it, and edit, or again, just claim as their own.
A.R., lack of an undo can be good in some cases, either that it can make you be more careful and work harder to produce something good, or in the other extreme, it can teach you to correct, hide, or perhaps even make something better from your mistakes. That said, I wouldn't want anyone to ever take my undo away from me, and when I'm not working digitally, I do miss it like crazy sometimes. (I know I'm not the only one who's tried to Ctrl-z away from my computer.)