The question will be what happens if Thornhill doesn't get its own subway now! Peter Kent has been very proactive but if he can't get Flaherty et al on board, if it stalls, people will be pissed.
As for this whole "I can't believe the subway is going to Vaughan..." thing, I'll just say this:
Toronto's transit planning has been lagging for decades and that's created two problems: underserved dense areas; underserved, fast-growing, contiguous suburbs. It's POINTLESS to argue that one is more important to fix one than the other.
If you want to say "we should deal with built-up areas before this mythical downtown" I'll counter that if that downtown gets built WITHOUT a subway it will be same sprawling suburban mess we've been trying to kill. Build the subway first (as should have been done elsewhere) and you have a chance to build a real, transit-oriented community.
And I'll be totally right - and so will you. Because this is not a zero-sum game. As to WHY one is getting built before the other there are two answers:
Finite funding and politics. Clearly if the two subway extensions were being funded along with the DRL and, for the sake of argument, Eglinton, no one here would have anything to bitch about. but as soon as any one of those gets left out, someone has a totally legit reason to bitch.
So, to sum up, complain all you want - you're right, but you're also wrong. And so am I. Doesn't change the fact the Spadina line is getting built and Yonge probably will soon too.