Tomcat is a WebContainer and only war deployments are supported. For JBoss ear deployment is not supported with Postgre SQL as its not tested and coded to support it. During Server Start you will get issues related to DatabaseException as query generation is not supported.
My question is more along the lines of why is my choice of database (PostgreSQL) impacting my choice of 'ear' or 'war' install. As far as I know, PostgreSQL supports two-phase commit since version 8.1 and secondly what do I lose (functionality, performance, security, connectivity to other protocols etc.) by using "war" files instead of "ear" files.
From what I have read, PostgreSQL supports dynamic SQL.
As explained, its not if DB is supporting 2 PC or other functionality. The CodeBase(Pega here) also should support the logic in relation with Application Server Containers.
Ex:- Each DB will have its own way DateTime & Function Calculations, to support with each DB like PostgreSQL or other DB the core logic also should understand what DB is expecting and what response DB would be giving. In the same context, each Application Server will use its own libraries to calculate the input/output.
With the above, JBoss with PostgreSQL is supported for WAR deployements for now. You will see many below exceptions like below if you start JBoss with ear & PostgreSQL. Hope this helps!