Your metadata is yours, and Apple is not stopping you from doing anything with it. A lot of it is already in the m4a file anyway, using either ID3 tags or some newer analog to them. As for whatever metadata is stored outside the music files themselves, iTunes actually gives you all the metadata you need: it shows you the metadata plainly. What they don't do is maintain a requirement that any arbitrary device or program can reliably access that metadata, i.e. by keeping it in a consistent, well-documented format. That's an engineering decision, not a moral imperative--it allows them flexibility to do things their way instead of worrying about breaking backward or third party compatibility.

Apple's margins on iTunes are pretty low, when you consider how much they have to pay out to record labels and credit card companies even before paying for their own infrastructure. Digital media is high-margin in total, but only if you can realize all the profit. The record labels can do that, but Apple can't.