In order for a database to be supported it must support Stored Procedures, Views and User-Defined functions.  Does Postgres support all of these as SQL scripts?

Well, I took a day and tried to add support for PostgreSQL.  Things were going well in that I was able to create 170 tables, 314 views and 26 functions.  The project died when the Npgsql Data Provider for .NET failed to connect to the PostgreSQL database.  At first it was a problem on the database server side, but I fixed that and I still cannot connect.  It would appear that .NET driver is not ready.

There are other issues, such as lack of support for GUID generation.  I've seen some hacks, but I am not encouraged by them.  The sad part is that the PostgreSQL community clearly does not understand the importance of a GUID. 

The last issue is of licensing costs.  Are you prepared to pay $400 per user?