I had a chance to talk to a friend of my at the OU who is doing research on the Tate's programme for kids and she tells me that the Rothko room IS at the Tate Modern. She described to me where it was, and I'm SURE that I have been to that part of the museum before, but I guess I just missed it. And, of course, as the Tate Britain is (duh) only BRITISH artists, of course, Rothko isn't there. I'm an idiot.
But, now I'm confused. This seems to indicate that this is an old display...
Here is an article about the Rothko Room..
So, back to the Tate Modern, although I'm not sure when I will get there. One of these days.