postgres-9.4 is available in ubuntu 14.10 and later. If you're in 14.04 or 12.04 (current LTS versions), you have to use the postgres-maintained source. The process isn't super-simple.
Node moves fast, sure. I'm not sure I agree with your "crazy breaking" modifier there: I regularly do dev work against the latest 5.x branch of node, and rarely if ever have to worry about breaking changes. Then again, I'm just doing plain old restful api and business logic stuff, so maybe if you're dealing with the c++ interface it's a different environment.
Even still, I think it's easy enough to see from our disagreement over "too fast" and "quite sensibly" that there's plenty of ways to be a programmer. Rapid improvement can be kind of exhausting (especially if you get behind) but it's also a great way to see new ideas emerging. One of the things I actually love about the javascript world is how quickly things move. Things evolve very quickly because there's so much churn, speedy releases, pressure for mindshare, and so on. It's fascinating, both technologically and sociologically.
It ought to be pretty straightforward to say "apt-get install nodejs-5.3" and have that Just Work, but by the time the curators get around to updating their packages, you may well be a month or three behind. (again, unless you've updated your sources.list.d to include the nodesource repo).
So yeah: curated package managers have a place in the world for sure. But the trade-off here is that you're not getting the Latest and Greatest. Joyent tried to Slow Things Down with the 0.10 branch of node, and you see where that got them.