The difference between "futuristic" as an esthetic and designing a plausible future has a lot to do with looking at the present and the past - how is technology actually applied to the way people live, how have people adapted to it and how is it adapted to a world that already exists.
One class of futuristic sf design which makes the fissure between the two clear is all of those evocations of future versions of Los Angeles or New York or other major cities (like London, LOL), often supposed to exist in fifty or one hundred years, which consist of nothing but soaring new constructions. The designers are pleased to assume that everything currently existing is just bulldozed flat to make way for mile-high space needles.
Another real good example is "futuristic" costume design. Theiss designed "magic" clothing without apparent fastenings or closures. When I get dressed in the morning, though, I make use of laces, buttons, snaps, zippers, and occasionally Velcro. The newest and arguably most "magic," Velcro, is about sixty years old; lacings are at least
five thousand years old and
both are in daily use all over the developed world. If I'm envisioning plausible, likely future clothing as opposed to "futuristic" then I'm going to use laces and buttons and whatever else along with "magic" - because there are esthetic considerations beyond the utilitarian that are integral to what people choose. That's called "fashion," but the reverse is also true: there are practical considerations to what people choose that trump esthetics. There is a reason that we don't live in a Frank Lloyd Wright world, among them the fact that we don't very much like leaky roofs.
The design of any age synthesizes the ancient, the traditional and the new, the practical and the fashionable and the innovative.
Now, in artistic design for things like, for instance, the early art for
Space Command you see artists like Doug Drexler talking about futurism while evoking mainly the "Space Age" design heritage of the 1950s and 1960s. There are specific reasons for that with regard to
Space Command, but it's nonetheless true that when people talk about futurism the examples seem to quickly turn to exercises in nostalgia - looking backward.
This is an awesome Facebook page, BTW:
http://www.facebook.com/SpaceAgePropaganda