For a CPL holder then going onto commercial flights they will then have to undergo compnay training and standisation and also whats called an operators procedure check which is along the lines of what G has mentioned.
The problem with adding more things is that the cost becomes ever increasing.
Most comercials these days head straight onto twin engined work.
Personally i have only ever been tested on PFL's twice. My intial PPL was in FL and wasn't tested in the PPL test. FI flight test and then the renewal were the only ones because I did the CPL in a twin.
The CPL is a basic license to learn. In no way is it the end of the process, the company then takes it further with what ever hardware you are flying.