"The future is already here, it's just not widely distributed yet."
A quote from William Gibson, famous science-fiction author and futurist. Gibson started out in the '80s creating the cyberpunk sub-genre of SF - arguably the first wave of recognition in the SF community for the computer's revolutionary effect. Cyberpunk is often irreverent and byzantine, seldom distant, and nearly always noir. These characteristics do a pretty good job of defining the future this genre foresaw: complex, similar and chronologically near to our own time yet changed in many ways, and dark.
Why didn't Gibson and others, such as Stephenson and Jeter, extend their cyberpunk narratives further in time? After all, Science Fiction has traditionally been about detailing scientifically plausible futures for various purposes like social commentary, gedankenexperiment, or simply prognostication. Restricting your work to the near future as opposed to the billions of years which lie ahead in the existence of the universe seems to unnecessarily minimize the palette. The question only becomes more urgent when you consider that Gibson has more or less gradually worked closer and closer to the present with his works. Actually, some of his most recent work is actually set in the present, possibly even the near past, ala Pattern Recognition and Spook Country.
The truth is that what would seem to be a gradual collapse of one of the genre's defining traditions is instead an increasing acknowledgement of singularity. The closer we come to the "event horizon," the more the rate of change makes reliable, usefully-detailed prediction impossible. Few authors of the 1950's would have pretended to be able to reliably extrapolate the technologies and societies of a thousand years from now because, as in chess, it becomes difficult to see a certain number of moves ahead, no matter how deterministic the system happens to be. When the rate of change increases to include the same number of "moves" in a tenth of the time-frame, you must adjust accordingly.
(Let me qualify the assertion about SF authors and predictions. Yes, there are quite a few stories out there that find it no great problem to attempt a prophecy thousands, even millions, of years out. These stories generally fall into a few categories:
1. Those stories which use the distance in time to purposefully separate their narratives from that of the present so that little adherence to the legacy of present circumstances need be heeded.
2. Those stories that invoke special circumstances to indicate a massive slowing in the rate of change, such as stasis fields, civilization reboots [you can argue about the implications of this one], civilization stagnations, or even alien enslavement.
3. Those stories which are dishonest or misjudge the predictability of the future. Barring the science of Hari Seldon, there are limits to what we can know about the world of tomorrow.
4. Those stories with no treatment of the history constructed by human civilization on Earth [ala Star Wars].
Remove these special cases, and you should find the pool well-thinned and more amenable to the earlier assertion.)
Science Fiction, therefore, is more than ever the genre which predicts not what the distant future will be like, but is instead increasingly concerned with tomorrow and later today. Gibson's quote sums it up - the rate of change has gotten to the point where science, technology, and society advance so fast that most of us are left behind in some facet or another. Moderns such as ourselves are left in the curious position of attempting to predict what our present day is like.
The sentiment is insidious and shared. In the July 2009 issue of "Asimov's Science Fiction," we find Robert Silverberg (in an otherwise worryingly narcissistic article) writing that "we all live in the far future, these days." Certainly Ray Kurzweil would agree, with qualifications. He has focused his mind on getting the next twenty to fifty years right in terms of scientific and technological advances in several specific fields, but has had little to say about everything else. As with the rest of us, he lives in a present he only partially apprehends.
Science Fiction is the genre that deals with our visions of tomorrow, which have now become the visions of today. If we want to understand our present circumstances, it is fast becoming imperative to look to the one genre which is seriously concerned with interpreting that predicament - Science Fiction.
An aside: I hear voices in my own head suggesting that non-fiction, too, can answer this question for us. Without getting overly poetic or philosophical, only a short retort is possible: fiction can honestly provide a hypothetical special-case scenario with depth and detail, while non-fiction must abandon itself to do the same. Of course it is important to understand the broader hypotheticals as well, but as our lives seem very special-case to us, fiction is often the more accesible avenue to grokking.