I have dealt with many applications that use SQL Server Express in production. Those limitations aren't even brushed against with small CRUD style apps. When you are only really serving two or three users and running maybe 100's of tps it's perfectly fine. Postgres is a wonderful database but I can't coach over the phone the average person off the street who is not a sysadmin to get it setup properly, but for SQL Server more than any other DB I certainly could.
I've been using the 'Express' version of MS SQL Server in production for some years now with a handful of small clients, including my current 'in-office' employer. It's not hard to setup a 3rd-party backup solution, and - touch wood - I've never ever had any issues with either the databases or the dependent applications.
No doubt other databases might be 'better' in various ways, but the Express version really is nice to work with and (yes, sorry to admit) it's an easier sell to customers than non-MS solutions (at least for me).
We've got 10-12 users connected to a SBS 2013 server with a couple of RAIDed HDDs and 8GB RAM, and - yes - the SQL Server service pegs out at the maximum allowed RAM (which I think is 1GB or so) pretty much the whole day. However the performance is deemed much more than acceptable, even though no doubt a lot of query results are getting booted out of RAM way too soon.
We've still got a trick up our sleeves in terms of performance boosting by moving the server to SSDs instead of magnetic drives.
FYI all my other clients running 'Express' consist of small companies with 10 or fewer users, and they are more than happy with performance (or at least aren't willing to pay the large MS fees for a 'proper' version of MS SQL Server).