The thing is, Nick, that most players are most comfortable RP'ing in a world which is reasonably similar to the real one. It's just easier that way. Many of us, myself included, struggle to understand what is going on in the world of science currently, which means the prospect of RP'ing futuristic technologies goes over our heads and out of our comfort zones!
It seems to me that people are the most wary of technological futurism in the military sphere. Perhaps this is because, as Selcrus said, "a certain sort of people will always want to play with those lasers and mega-cyrbogs to win all the time"! In my experience, people are generally more relaxed when it comes to technological futurism in other spheres. For example, I recall human cloning being RP'ed (or at least very strongly hinted at) in the past, and nobody complaining. I also recall players posting pictures of very futuristic looking buildings and cities, and nobody complaining about that either.
Speaking personally, as a player I have come in for criticism over technological issues twice. The first was when I established Ibutho, a technologically backward African/Zulu nation. People complained Ibutho was too backwards and that I should make it more modern. At the time, though, Terra did not have any actively RP'ed third world nations, and I felt strongly that Ibutho's backwardness enhanced rather than detracted from realism, because the real world does have poor, backward societies. I signed Ibutho up to a
Framework for third world realism to try to restrict certain legislative options which would be unrealistic for a third world country, though Ibutho has since withdrawn from that.
The second occasion was more recent, when I was involved with a RP about Luthori having developed a space missile system. Here, the criticism was in the opposite direction (ie. that the technology was too advanced). I felt that concept was futuristic, although not *too* futuristic because with today's science, accomplishing that would not be so inconceivable if the real political will/organisation was there to do it. It might even be a reality today if the Americans and Soviets had not agreed to demilitarise space during the Cold War. Others, though, judged differently, and that particular RP was brought to an end. Which I didn't massively object to, to be honest, but nevertheless it is an interesting example to look at when it comes to discussing the "boundaries" for technological advancement.