overread: Errr I think you might be splitting hairs with the definiation of sci-fi. Generally speaking most would consider Dawn of War/Warhammer 40K to be science fiction - its futuristic fiction (with space ships, aliens and suchlike) so yeah it fits the general sci-fi requirements.
And yes its tactical, but its still real time strategy; it just does not involve traditional base building (which is not a requirement for RTS, just a typical component of it).
It's not splitting hairs when the creators don't consider it sci-fi, when it includes numerous fantasy elements and when it's just generally nothing to do with sci-fi. Space ships and aliens? - Star Wars has space ships and aliens in it. Yet it's pure swords and sorcery fantasy. Space ships and aliens might well be an indicator that what you're looking at is sci-fi, but as Star Wars and 40K prove, that's not always the case.
The reason why these things are often considered sci-fi is because one of the most popular forms of sci-fi is looking at what our future might hold for us. Something neither Star Wars or 40K are trying to do. 40K is about the future of a fantasy world. You don't have to look far to see the fantasy is still very much in tact.
Tactical = individual skirmishes. Strategy = overall war. Base building is kind of cheap in a lot of games as it's not something you'd really do on the front lines (Supreme Commander and Total Annihilation are among the few that make sense of it). But it does at least help justify calling it strategy.
Tactics is what DoW2 is all about. You could argue that the in between mission map implies strategy, but unlike Dark Crusade, it doesn't really provide any choice beyond 'do you want to do some bonus missions or not?'
I'm not knocking DoW2. Far from it. I'm sticking up for it. Because when you apply labels to it like RTS you're applying expectations. And that's why a lot of people immediately went off the game. They went into it expecting an RTS.
It's like selling a Ferrari as a family car. It might be great on its own terms for its own purposes. But there's no room for the kids and groceries though. So as a family car it would suck.