Why does the heal skill govern the increase in negative spell power, and why is the heal skill not a class skill for the wizard, a class that if the player chooses to go PM, needs more negative spell power?

Spellcraft aside, every other exception (rust, sonic, reconstruction, positive) lines up with the corresponding class’s class skill.

I know it’s a minor quibble; we’re talking 8 spell power. But it seems like there was zero creative thought involved with this decision. I’m wondering what others think. I’m also wondering if this can be changed.