I think expectations from artwork have also changed over the years. The same demographic might have given you a preference 20 years ago, that is no longer what they would ask for today. Regardless of style preference, and media used, there is what's "modern", and what's "outdated". This applies even to a pencil sketch. Of course artists are constantly revising what's modern and what's outdated, so it's not exactly black and white there either.
I am imagining myself, buying the next edition off the shelf, brand new, the pages are still crisp and the new book smell wafts into my nostrils before I even open the book. I'm filled with excitement. Let's assume for the sake of argument, there is no cover art (ala 3e PHB), and first thing I do, as with any book, is open it up and look at the pictures. If the first thing I see is a black and white drawing of a tubular dragon with a goofy football shaped head and buggy eyes, I will likely drop the book as though it's burning my hands. Having said that, this probably would not have been my response 20 years ago. So the dragon art failed to meet a current expectation.
For the sake of argument, let's say 4e art is my "current expectation". If the first picture I see in the next PHB is the iconic dragonborn fighter from the 4e PHB cover, cut and pasted exactly the same, what will my reaction be? Well, I'll probably put on a big frown of disappointment. But that was the base line for my current expectation, yes? Well, apparently not.
So ideally, the art direction has to take what might be the presumed current expectations, and drive them some distance, into a new neighborhood, that has not been fully explored, that is fresh, and yet, still in the same universe of what we want to find in D&D artwork. I obviously don't want to see Picasso or Dali in a D&D book (though when I think of planar travel a few Dali's might make an appearance in my imagination).
So, long and short of it, it's not about the style, or media, or culture, or generations, it's about expectations, and hitting the right balance of borrowing a subset of elements from those expectations, and building a new picture. Of course, good luck figuring out what those elements will be.