Yeah, because they can do arithmetic really fast?

I wouldn't consider adding 1 to a register here and there and taking some conditional branches "math". Modern math (usually) involves thinking about theorems very hard and then writing proofs for them.

Algorithms have existed in the world of mathematics thousand years before computers were invented. From this point of view, computers are just a way to speed-up things.

If the Euler algorithm was discovered today, should it be patentable? What about the FFT? Is there any substantial difference with any "modern" algorithm, like the DCT or arithmetic encoding?

I already said algorithms can be plausibly called math.

Lots of software, and software patents, have little to do with novel algorithms.