I agree about Winter Silks and Anthropologie. However, the reason good slips are so hard to find is because so few people wear them now. Even with many bloggers, they display photos where one can see the outline of their body through the dress, like that is somehow a good thing.
Regarding Linda's comments, though, support garments aren't anything new, nor would they be available if they weren't in demand. I see no "trend" mainly because they have always been popular. There were paneled girdles in my grandmother's and mother's time, and women often wore corsets prior to that. The desire to make one's shape closer to the "ideal" has always been around, and there have always been various types of support garments to help women achieve it. Again, if no one bought it, they wouldn't have entire sections of them in stores.
I do agree with you about keeping healthy, but I have loose skin after pregnancy, and all the running and sit-ups in the world aren't going to make that go away. A friend of mine is a size 2 with a "crepe paper" tummy (bumpy). Wearing something to make sure it stays smooth under dresses isn't giving up; it is simply reality that I will always have some bumpy skin on my tummy. I suppose I could embrace it and be bumpy in my dresses, but I choose to smooth it out instead.