Well, on my iPhone I barely use half of the 16gb available; I don't see the point in keeping many files on it since I stream all my music, (cheap, fast and unlimited data) don't play games or hoard photos for anything more than 5 minutes 'til I upload them.
I have no music on my phone either. I have however managed to accumulate over 25GB of other files, such as photos, videos and documents. I'm not one to keep masses of SMS or other clutter, but I do use my phone as a working device. It would be unheard of to have a pc with an 8GB hard drive, so those of us who use our smartphones as portable computers do tend to need the 32GB model (if not more).