Yup. Different jobs at game companies are getting more and more specialized. It's getting to the point where game environments are getting too visually detailed for most traditional level designers to handle. If done correctly, the workflow combination of a separate artist and level designer can actually be faster and produce a better, more polished, product in the end. This also leads to the artistic theme of the entire game being more consistant.
For instance, look at a game like UT2k4. A very large portion of the maps were made by a large amount of different people. As a result, you get a game whose maps are very inconsistant. It works for UT2k4 because it's just a crazy game with no clear visual theme anyway. One minute you're fighting on an asteroid with two towers and the next minute you're in and Asian setting. But the game tends to feel less like one whole game and more like an assembly of mods.
HL2 was so polished and looked good because they did separate the level design from the artist tasks. Same with Doom3. Farcry. These current gen games, IMO, show how the roles of artist and level designer are breaking up and how well it works out if everyone is talented and specialized. Just think of next-gen engines and how high-poly they'll get. It's almost too much work even for the level designer that can do relatively high-poly modeling and 2048 texturing.
I think in the next year or two, level design and artist will fully separate across the whole industry because of the boost in has-to-be-modeled-detail-because-brush-can't-do-it. Brush, as a visually appealling tool for the LD, is dying. Brush is going to get to the point where it's only really useful as a method for optimization. But you say, "What about HL2 and Doom3? There's still a lot of brush there!" and I'd say that you are correct and it works well, but the next couple of gen leaps in engine tech and hardware tech are going to make HL2 and Doom3 look like Quake1.
And don't worry, it's not like the level designer doesn't have anything to do anymore. He's now plenty occupied with gameplay/mapflow creation, blocking out the entire game, scripting sequences, and most important of all, making the game fun. Fact is, most LD's are mediocre at modelling and texturing. When a company is trying to create the best possible game, who do you think will get the task of modelling the statue that goes in the courtyard in the map? Artist, because he'll do a much better job at it.
Gearbox does it this way and as a result, the game is better, visually and consistantly. And I still get to do a big portion of tradional LD things. I didn't make the tree, but I get to put it where I want to, and it looks better than anything I could have created myself.