MS Sql Server not even mentioned. This tells us there is a whole world almost totally omitted from discussion on HN: "Enterprise"
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While in a way it's just a corollary on the expensive bit, the license compliance of the same becomes such a monumental hassle as well, and is just an enormous time waste for everyone involved. For everything you want to do there's a probing Microsoft or Oracle salesperson trying to shake you down a little harder.
Go with Postgres et al and you can be geographically distributing, horizontally and vertically scaling in a million ways, making whatever warm of cold standby or recovery system you want, and so on. Even when the pricing of the enterprise offerings were tolerable, the system around constantly extracting a pound of flesh is so overbearing it induces opposition.