^ Yeah, he's not Superman, after all.
"
What?! Earth is in crisis
again? Blimey, but we were just there! I'd really rather save the inhabitants of Moldavon XIV from the warring worms in the year five billion. Wouldn't you? Moldavon XIV. Happy people, lovely weather, peaches the size of pumpkins..."
But he does have a time machine. No reason he can't do both.
(note: This is not all directed at you, but rather the notion that the Doctor could or even
should have popped up)
Which is an oft brought up argument, but one which doesn't fit with the model of time travel/personal timestreams explicitly used by the show.
He can be in earth's past whilst this is happening in its future. From the perspective of his own timestream, and that of his companions, it's happening at the same moment. The show tells us this all the time. Perhaps the 456 event is timelocked, or it *needs* to happen for the sake of history. Blahdy blah blah.
I can quite accept that The Doctor may simply have been unable/unwilling/unmotivated (unaware) to turn up, because the alternative is that he *does* show up (which he didn't) and that would have been fucking rubbish. Every time someone complains that he didn't save the day I almost die a little inside, because the show gave us the arguably some of the best hours of science fiction television in a decade, and some people think it could be *improved* with a shitty, nonsensical, deus-ex-machina conclusion which would have served no decent dramatic purpose and cheapened the whole damn thing.
Rant over. It's 4:10am and I'll be surprised if any of that shite made sense.