Superluminal drive in Halo is a fact - especially given the novels. I get the impression they also have a pretty far reach; the autumn got there, and survivors got back, fairly quickly (not in centuries or decades or years, I know, though I can't remember the exact travel time), but the thing was far enough out that, after seemingly building something of an empire, humanity still hadn't come close to finding them. It seems likely that, if there was an inhabitable planet eleven light-years away, there would have been some human presence there.
Didn't something, a book or such, include a star-chart? Couldn't that settle this debate? If Tau Ceti's within humanity's borders, shouldn't something have been there?
And the light-speed limit does kindof assume Earth wouldn't even bother to send some kind of superluminal probe out to them.
I doubt a world held in slavery, as I believe Mars was, would be a technology center of the Sol system - by the time either the fusion pistols or the MADs could be mass produced, wouldn't some documentation on the technology have at least left mars?
For that matter, what about when Durandal goes back to Earth. The Sol he returns to seems to be in ignorance of FTL, doesn't it? And this is centuries later...
