In movies like that realism is key, and the better the costumes, the more invisible they will be. They have to act subliminally. You have to make a conscious effort to notice details like clothes that seem to be slept in, or one character wearing slightly different things than another in a way that communicates subtle differences in class or taste, but these are exactly the things that call for the greatest skill for a costume designer.
But everyone notices wild extravagant costumes, or elaborately distressed and filthified costumes, in period pieces or sci-fi. And in a movie like Black Swan, everyone notices the ballet costumes. They’re “pieces”, separated from the world we know, and they announce themselves as costumes
I'm not educated on the specific question of costuming, but it's clear that there are some obvious issues here that reflect on the broader issues of movies, art, and realism. (Or, if you prefer, "realism.") Oscar season is a time for perpetual consideration of whether the role of filmmakers is to reflect reality as closely as possible or to make reality more outsized in order to entertain and make artistic statements. Obviously, here, I'm not so much interested in grand spectacles like Avatar, although it's interesting to think of what a movie like that thinks of as being more "real" as it pursues ever more advance 3-D, computer graphics, and visuals. I think the real question is in the world of drama, and movies that are trying to more or less portray events, characters, and places that could exist in the real world.
Is the regard for Daniel Day-Lewis a product of his ability to disappear into a character and show us what real life is like? Or is he a beloved ham, who wins the plaudits he does because he gives us the thrill of the scenery chewing we secretly love? It's the old "presentational/representational" school, if I'm getting those terms correctly. It's often discussed when considering the divide between British and American acting-- you hear the line sometimes that Britain makes actors, America makes stars. Embedded in that, I think, is both an acknowledgement that good acting should in some sense be antithetical to a star system, but also that what people pay for, being entertained, often involves transcending being a realistic depiction of life. Of course, Oscar has long ago thrown in his lot with capital-A, showy acting; the Academy seems like it will always prefer bravura, meaty performances like Sean Penn in Mystic River over quieter, naturalistic performances like Ryan Gosling in Half Nelson.
I shouldn't pretend that I'm neutral on this score; I tend to prefer the more sublimated style of acting where the actor seems to disappear into the character. It says a lot to me that Heath Ledger was rewarded by the Oscars not for his quiet, wounded, and complex portrayal of Ennis del Mar but for his madcap turn as the Joker. (Of course, Ledger's death probably has something to do with this too.) It's not that I'm asking a Batman movie to showcase restrained character portraits. It just seems to me that while the Joker portrayal is more fun for the actor and has more obvious, look-at-me-moments, the performance in Brokeback Mountain is a great accomplishment.
However, there is something that complicates my feelings on this issue: I like almost the opposite in fiction. Obviously, there's a world of difference between realism in writing and realism in acting. But I've always preferred novels and fiction that were unafraid to move beyond the cramped definition of realism. One of the many virtues of Ben Marcus's notorious takedown of a certain absurdly narrow definition of good fiction is that it called into question the basic assumptions of what "realism" really means in the first place. It's an interesting challenge to myself: why do I want fiction to transcend traditional form, but movie acting to remain a matter of representing real life in a reductive sense? I imagine it's because of my dedication to the avant garde, and my natural, somewhat silly resistance to what is commercial. In fiction, what is prized as realistic in a narrow sense is also what most people buy and what publishers and the literary critical establishment insists is the only true way to write a great novel. In the movies, it's the quieter, more nuanced performances that are seen as belonging to an indie, art-house culture.