The power of the other tools mostly shines in large scales. For most applications, though, performance of postgres more than suffices.
I tried to use rabbitmq for a small app, installed it, configured it and then it didn't work. Spent a day jumping through hoops getting it right.
Dumped it and used postgres, in half an hour. Worked like a charm.
Would your app run equally well with sqlite?
Sure, best not to overcomplicate early if you don't need it.
PG is great and I work with it daily, but it's also not a problem to think about scale early and at least have a notional plan for what to and how to know when scale is becoming an issue in your system as you're designing it. Even PG is overkill and sqlite is more than enough for some of my projects.
There are a lot of specialized tools available, but you definitely don't need to put every one in your toolbox. Experience and observation help you make those edits -- and of course there's almost always room for improvement, but "good enough" definitely exists (until it doesn't anymore :D).