It's what I said about needless arc and hype - if they'd just done the episode and moved on we'd all be thinking "cool, they live out their lives in the past" but by going on about the finality of how they can never see the Doctor again, it just makes us go "but they can if..." Moffat's a great scripter, but their grasp of publicity and guiding the audience is totally borked.
That explains things. I haven't been following any hype or whatnot, so I just went with what the episod showed us. It was clear during the episode what they were going for, which was a definite sense of finality, so that's what I went with. And I don't think I've ever seen a time travel story, without the possibility of shooting gaps in it, so I'm not going to be bothered too much by the typical time travel wackiness.