Its been mentioned previously, although I do not think last night, that sometimes the Doctor is not on Earth (as we know) and not even reachable.
As for why no Sarah Jane...BBC politics, I would think. Sarah Jane is a kids show. Torchwood is after watershed. And they have said they will never cross them over.
They broke that rule, a bit, when they crossed them all over for Doctor Who finale, but that was an exception.