Are there links to licensing costs? Are there regular client access license costs as well? So... if there are costs for licensing, then converting from postgresql to mssql is a little harder to swallow.
This is correct. SQL Server licensing is not changed. The major benefit is being able to share a single infrastructural OS for application and DB - it is not uncommon to see Linux app environment and Windows DB environment in a lot of large organizations.
The secondary benefit is removing the Windows OS licensing cost.