That's my main argument for using Postgres:

1 - At the start of your project's life, you'll want it because it's free as in beer. Except for ease of developping (where Postgres is also great), nothing else matter.

2 - Later, when you need some performance, even if you have a usage patter where Postgres is slower, you'll discover that the price of any of the other DBMS is highter than just adding hardware. Thus, free as in beer wins again.

3 - If you get huge, you'll discover that free software is a big deal, and the limitations of the proprietary DBMS add a huge amount of drag. Free as in speech wins now.