Because the mathematics is basically distilled, formalized art of precise thinking. It's the art of manipulating and morphing mental models. It's as much about numbers as astronomy is about telescopes ;).

Forming a model might not involve precise thinking, it often involves lateral thinking, at least with me.

I heard that computer science was more of a subset of music than math.

Higher math requires a great deal of lateral thinking. Also, music an math are often closely related but I don't see the connection between music an say computer vision.

Computer vision practitioners do mostly math, are we calling them computer scientists also? Sheesh :). Whenever I get in the same room with one, we are talking completely different languages (and we do have a sizeable computer vision team in our lab).

Computer science is the study of algorithms, information systems and anything that is computable.

Mathematics is the study of formal systems, eg proofs that can be derived from axioms using algorithms, i.e. a specific type of computable system.

Therefore, mathematics is a subset of computer science.

Math includes the study of non computable things. Also, Math includes chaos theory which is more than just a formal system.

EX: computable numbers are a subset of all numbers. http://en.wikipedia.org/wiki/Computable_number

mostly kidding. but presumably the theorems about non-computable numbers are computable and therefore you're still working with computable things?

That's what a Maths degree is all about! I guess Maths emphasises the model and CS emphasises the mechanisation.