A quote from Zen Action, Zen Person:
When I asked a Japanese friend why Shakespeare is so popular even among the Japanese (who know his work mostly through translation), he replied that Shakespeare is universal because he is so perfectly Elizabethan. [Emphasis mine.]
I've talked before — here, here, and here, at the very least — about how every work of creation is a product of its moment in time and space. So are the creators themselves, and the audiences that experience both those creations and those creators.
One of the reasons I recommended The Tale of Genji in my "Non-SF&F Writing For SF&F Authors" list is because it is so perfectly,well, Heian. It is an encapsulation of its moment in time — not just the clothing or the pageantry, but the attitudes, the states of mind, the expectations one could have about one's world in such a milieu. These are things a book is worth reading for, at least as much as the plot or the superficial details or the setting.
Every book written in this day and age — even the ones that are not set in this day and age, and maybe especially those books — are no less products of their moment in time as any other. The glimpses we've been getting of Man of Steel hint at a Superman story that might not have been conceptually feasible in 1979, or even before that: our cultural conversation about superheroes was still relatively primitive compared to what it's become.
In the same way, a story of the Roaring Twenties written today (as opposed to in 1922) will not, cannot, have the same attitude about its material as opposed to one that's a product of the moment it depicts. This was the problem I had with the film version(s) of The Great Gatsby: the book was not celebrating the excesses of its period but lamenting them, and the movie(s) seem to be only able to put the book on the screen by putting all the glitz of the era up there.
Fantasy and SF seem to embody two different poles for this problem. Most fantasy is atavistic — in the sense that it thinks about ways things could have been once upon a time (Tolkien), or imagines a here-and-now rooted more in a past era's understanding of the universe (steampunk). SF is rooted in a forward-thinking view of things, but is doubly a product of the moment it's projecting forward from — as attested to by the food pills, world governments, flying cars and slide-rule wielding scientists of SF from previous eras. Those things can limit the work, or in time become part of its peculiar charm. Nobody thinks of Metropolis as being cutting-edge in either its technological or sociological insights, but it has acquired a timelessness of spirit that exists apart from any of those things.
In the short run, a story has to embody its moment in time in order to be coherent, or salable. Most audiences are not in the business of being avant-gardists. But in the long run, every story has no choice but to embody its moment in time. We might as well make the best of it, and become as perfectly Elizabethan as we can — for through that door might be the only road to real timelessness.