JAA's & Australia's licencing system is mostly embrasive - all your aircraft privileges are included in each level of licence as you obtain them, subject to various recurrency/renewal requirements. Have a PPL for SEL & get tested for a CPL Multi-engine Land and the SEL privileges are included with the CPL.
The FAA systems is exclusionary. Have a PPL for SEL and get tested for a CPL Multi-Engine Land and you will have CPL privileges for a MEL, and only PPL privileges for SEL. That's why in the US you need to do more flight tests (checkrides) to gain MEL, MES, SEL, SES privileges at each licence level.