Because that's a handicapping system in another guise.
Quite right! Remember when all but the top 4 in the WCC got a third driver in Friday practice, which in 2005 spearheaded McLaren's title charge. Quite how the FIA would have dealt with that in 2008 is a question thankfully left unanswered!
Either way, whats to stop the FIA/FOM giving the 'brands' a little push. Looks like Lotus are poor here, Ferrari poor there...