yes they do this to get traction over the rear wheels which is really light as it is... not to mention they typically to go in a straight line, the physics change drasticly when you turn the steering wheel.
I promise you with out changing alignment/chassis dynamics simply adding more weight to the front of the car will cause it to exhibit more understeer. This is a fact.
Quote for truth, I see guys with S13's gut the fuck out of their interior and remove everything from basically the rear of their car and then can't figure out why the car pushes more. Huh? i wonder if its because the weight balance has shifted to the front now.
Balance is a key thing to keeps in mind, Hence why I leave my spare tire in while at events. It feels better with a bit of weight to throw around back there.