It would be a wonderful experiment to turn in that Thompson review to a handful of the arts editors at the major newspapers and see what they'd do with it

I don't think it would be published today -- even though there surely are people capable of writing on that level -- because it wouldn't pass the mass market test.
I think Paul has hit on the nub of the problem, that arts coverage was once written with the expectation that it would be read by the people who were interested in it. I write from the perspective of a daily critic, who's lived through the paper price hike that Paul mentioned and has seen space given to dance tank. We very rarely cover cast changes any more, and the idea is, well, only 2000 people saw it -- of course, much much less than that for experimental dance -- so we just can't give as much space to it as, say, "Fear Factor," which is watched by millions.
The notion that Everyone must be interested in every piece that is written is noxious, I think. The critic has always functioned, at least partly, in the way the medieval troubadour functioned. S/he has access to the arts of the day in a way that ordinary people -- even ordinary princes

-- didn't, and one of the roles is to say "You've never heard of this person, but what he's doing is very interesting, let me tell you about it." Or, conversely, "I know you all think this new play/ballet/opera/symphony is the finest thing going, but it's about ten levels below and 20 years behind what they're doing in Ruritania this season."
The space/audience problem doesn't answer all the complaints about daily critics -- one can be ignorant, unjust, or corrupt no matter what the space

-- but it's part of it. Another part -- and it's a big one -- is that the Pundit Class, the supposed elite/intelligentsia that runs newspapers today could care a fig about the arts. If it ain't Britney, they don't want to know. This is a huge change in our culture, and if I were running educational outreach programs I'd spend some time educating the future editors of America.
Another problem today is that there are so few papers, and many of the papers don't cover arts criticism -- because, like, you know, who cares? I the hell don't, as an editor might say. Criticism of several decades ago was more robust -- decidedly different opinions, clearly expressed, so you could evaluate the point of view. I wouldn't object to a critic saying, "Oh, finally. None of those silly Swan Lakes, but some really good cutting edge stuff" if there were someone else saying, "Why is a ballet company doing soccer this season?" I think the bottom line is that we all judge a critic by whether we agree with what s/he says or not, and how it's said is, for most people, less of a concern.
(And thank you, Paul, for your comment about my magazines. One of the pleasures of publishing them is precisely that -- we can write for people who are interested and knowledgeable about dance.)