Rookie questions, perhaps, but: A) Why do Macs need...

Rookie questions, perhaps, but: A) Why do Macs need to update so often, and B) Why are these fixes so massive (900mb for firmware just updated a month ago, and a 130mb update for iTunes). I'm not a die-hard Luddite, but K.I.S.S.- if it ain't broke... don't fix it. I realize there are security updates, but nearing a gb for firmware almost once a month? Oy vay...