A lot of anime does this too. I guess it's just generally weak writing, and a paranoia about taking chances with the property. One of the things I really liked about Battlestar was how characters had to choose something, every time. You gained a way deeper understanding of them by what they'd chosen to do when the chips were down - you could never go back to how things were. CONSEQUENCES. We need more of them in entertainment.
I'm not the biggest fan of Torchwood (I mostly just caught the finale), but one thing I liked was that there didn't seem to be many Deus Ex Machina tossed around until AFTER everyone had made their true colors shown.
Children of Earth did it two or three times too many, in increasingly contrived situations, but yeah, at least it did it.
Course, RTD's Doctor DID make the call on more than one occasion, it's just that he'd get saved immediately afterward. (Letting Rose die to stop the Dalek, then turning around and letting the Dalek escape to save Rose -- yeah, in the end Rose lived and the Dalek died, but you saw his anguish in making the decision both times. Ditto with letting the Dalek Emperor win in order to save Earth -- in comes Literal Deus ex Machina to fix everything, but he DID make the decision. The Time War is pretty much the only no-win situation where he made the tough choice and it stuck.)
Tangentially, one of the reasons City on the Edge of Forever is the best episode of Star Trek is that it gives Kirk that exact dilemma: let an innocent person die for the sake of the future of human civilization. And it doesn't cop out; he has to make that choice.
(Actually, in the end, the Doctor DOES make a choice like that -- [spoiler]himself for Wilf[/spoiler] -- in a scene that bears a more-than-slight resemblance to [spoiler]Spock's death[/spoiler] in Wrath of Khan.)
I was always hazy on this, but we've been following the Doctor since his first regeneration, right?
Well, technically the Second Doctor would be the first regeneration, but yeah, the First Doctor is supposed to be THE First Doctor. That was ambiguous early in the series (I think there's an earlier episode that shows multiple faces, implying they're all the Doctor, including some that aren't actually the ones that had been shown on the series), but at this point, yeah, all the incarnations that have been on the TV series are all the incarnations the Doctor has ever had.
So the first Doctor, that old, grumpy bastard, would likely be the man she'd married.
The relative ages of Time Lords in general aside, it's not too far-fetched. He literally became a different person than the man she'd fallen in love with.
But she wasn't around even when the series started. The Doctor's reasons for leaving Gallifrey have never been concrete, but they've always had to do with a kind of wanderlust that doesn't really lend itself to home life. (In the Time Lords' first appearance in War Games, #2's explanation for leaving Gallifrey is a simply and wonderfully stated, "I was BORED!"; #10 explained that every Time Lord has a different reaction to the Total Perspective Vortex, and while the Master's was madness, "I ran. I've never stopped running.")
Quick thought: this regeneration is a pretty clean sweep, but they often aren't. I haven't seen all of them, but quick review:
#1-to-#2 (haven't seen, of course, seeing as it's lost): companions are present and have to adapt to the Doctor's regeneration.
#2-to-#3: pretty clean sweep, but not entirely. Companions are removed and we don't even SEE #2 turn into #3, but the new status quo IS laid out: #3 will be trapped on present-day Earth.
#3-to-#4 (haven't seen): Sarah Jane present; status quo resets over the next few serials.
#4-to-#5: Happens in the middle of a major serial arc, but on the other hand, 2 of the Doctor's 3 companions show up for the first time in those serials. Davison comes in with continuity baggage, but it's very recent continuity baggage.
#5-to-#6 (haven't seen): Peri is present, but has only just joined up. A pretty quick change to the new status quo.
#6-to-#7 (haven't seen): Well, this was a FORCIBLE change into a new status quo. Baker's removed without even being invited to do his own regeneration scene; Mel's present but is a relative newcomer and only lasts about a season.
#7-to-#8: well of course this is a clean-slate one because it was the series relaunch. We see a pretty solitary #7; he picks up a couple companions just as he's regenerating, but they're both new characters. (This is also, I think, the second-longest regeneration sequence, after Tennant's very long goodbye, of course; while the Doctor's fatal shooting is wonderfully abrupt, his slow death on the operating table and eventual resurrection in the meat locker take up a good chunk of the movie.)
#8-to-#9 (haven't seen because it doesn't actually exist): up to the imagination, of course. At what point in the Time War did the Doctor regenerate? Was it right as he threw the switch that wiped out the Daleks and the Time Lords, or sometime before? In practice, of course, the '05 series was the most sweeping, clean-slate relaunch the series has ever seen (the non-canon Peter Cushing movies notwithstanding); RTD had a completely free playing field to set things up however he chose.
#9-to-#10: Rose is there, goes through the requisite disbelief as the Doctor regenerates, status quo is restored in pretty short order.
#10-to-#11: companions are dismissed (very slowly); Doctor is left alone on the TARDIS. It's totally Moffat's to do whatever he wishes with it at this point. That said, he's already set up a few beats he's coming back to, in the Weeping Angels and River Song.
I'm sure if I hit up Wikipedia for an hour or so and studied the different creative teams that worked on the original series, I'd gain more insight into why some regenerations were more clean-sweep than others. If I had to guess, I'd say the same writers stayed on as Hartnell transitioned to Troughton but not as Troughton transitioned to Pertwee, that there was a creative transition about a year before (Tom) Baker left...things like that. And obviously the reason the status quo stayed much the same between #9 and #10 was that the same people were writing the show.
Going to bed now, but I think this is a good topic; please share your thoughts. Gnight!