The draw back to using PDO for us would be that we would need to test and support all of the different RDBMS Systems that PDO can connect to. It's a pretty long list including systems like Oracle and MS SQL. other systems on the list are pretty specialized like 4D.
To be able to support these systems would mean purchasing licenses for them and doing the QA testing. The cost of the licenses alone would be prohibitive.
ok that makes sense, I didn't consider that