dvt : ´Some egghead tried to explain it to me once´
I´ll give it another try ...
It´s quite simple, for a swept wing aircraft inner wing means front of CG, outer wing means aft of CG. If you deploy spoilers on the outer wing, you reduce lift aft of CG which causes the plane to pitch up.
If you use ailerons, you add lift on one side and reduce it on the other, so the effects in pitch rule each other out.
An additional effect is that the airfoil pitching momentum (acting nose down for a positive cambered airfoil) is reduced if deploying spoilers. This makes some planes prone to tailstrike if ground spoilers are deployed, although they are on the mid wing and therefor close to CG.