this is much more the meaning of the statement, as SF isn'y merely Traveller, or SW and ST, although they are a part of it...Science Fiction allows a whole host of paradigms. Often, ones not explored in Traveller.
This isn't to say that they can't be...but that perhaps they SHOULD be.
That's the thing though - Traveller doesn't know what the hell it is.
1) Is it a generic scifi game? Or is it a scifi game set in the Third Imperium at various stages of its history (past and future)?
2) Is it hard sf? Or is it space opera?
If the answer to the first question is that it's a generic scifi game, then it should be presented as such. But it isn't. Its halfway there, but there are still too many limiting features that make it something specific rather than generic. T20 has a load of predefined, OTU alien races in the corebook, for example. The techonological architecture is rather fixed at the moment (jump drives, thruster plates, clunky computers).
But Traveller HAS produced several books that would fit right into the release schedule of a truly generic scifi game like GURPS Space or Star HERO. The original Fire Fusion and Steel, for example, is (IMO) hands down the most useful book ever written for a scifi GM (similar to, but better and more informative than GURPS Ultratech, I think). It's got all the options you'll ever need right there. DGP's World BUilders Handbook and GT:First In gave you all you needed to know to make worlds in a scifi setting. But those books were released when the Traveller line was getting pretty
specific - MT and TNE clearly had rigidly defined background settings.
So Traveller's been somewhat schizophrenic. On the one hand, you get Traveller books that present specific settings, like the MT Imperial Encyclopaedia, or the Traveller Adventure, or Rim of Fire, or Gateway Domain. On the other hand, you get books like WBH and FF&S which are built for a generic game. So make up your mind, Traveller - which are you, specific or generic??!
GDW, oddly enough, missed an opportunity. If CT was truly a generic scifi rules set, then why on earth didn't they use it as the backbone for T2K, Traveller 2300, and all the other RPGs they ever produced?!
QLI's approach of publishing different settings for the same rules is interesting - but I don't think it went far enough at the start. Ideally, the Traveller corebook should have been full of generic scifi rules. General character generation, combat/game engine, technological architecture, world design, suggestions for making your own scifi universes. All the alien races and technology and history and specific assumptions and details that relate to the OTU should have been split off into the Gateway Setting book.
Right now, QLI have got three setting books on the way, but from what I've seen so far it doesn't look like they're going to be using the rules in the T20 corebook as they are - there's a fair bit of modification going on in some cases, which shouldn't be necessary if the T20 corebook was truly generic. Ideally the core rules should be the solid framework over which the setting is built - one shouldn't really have to change that skeleton for each setting. But that has to happen because T20 was a bit too specific in its execution.
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As for what sort of scifi it caters to... I think it's fairly clear that it's generally supposed to be a realistic game with some unrealistic elements. The level of detail in the ship and star system design should illustrate that (especially in Book 6, FF&S and First In). But again, the schizophrenia shows through - you have realistic ship and world design, and people nitpicking over how much bloody
taxes need to be paid to sustain fleets, but you have psionics and evil space empires and 1970s computers?! Again, there are conflicting foci, and that's shifted over each incarnation of the game (TNE and GURPS tend to be realistic, T20 is more cinematic in style).
If it really is a generic scifi game, then it does need to cater to both extremes. But if it's tied to a specific setting (the OTU) then that has to decide whether it's hard-sf or space opera in feel, and it has to stick to it. And if fans don't like which one it settles on, then they're evidently going to have to find another setting to play in that they're happier with.
So if Traveller could actually decide whether its supposed to be a specific scifi setting or a generic one that you can use to build settings, or if the OTU is supposed to be hard sf or space opera, then that would be a good start in nailing things down...