The beauty of Apple's lineup right now is that there is an iPod and a Mac for almost everyone's needs and wants. Just because you do not want or need more than 30GB for your music, doesn't mean that others to not.
Does it really matter to you if I want more if Apple offers a product that meets your needs better?
I have an 80GB+ iTunes library and it is growing by the day. There are still a few hundred classic jazz disks that I want to get my hands on and I am sure that those will lead to even more that I will want.
There really is no such thing as too much music, however too little music is a bad thing indeed.