Adding RAM does not void the warranty on any Mac, except possibly the Mac mini, and even then, it's only void if you damage it in the process (unless you're a certified Apple tech), or install RAM that somehow kills something else. Think of it like adding a turbocharger to a car. If the rear suspension breaks, the warranty on that part isn't void because of the turbo (although some dealers may argue this), but if the cylinder head goes, you're SOL.