Sorry if this has been answered but I've been Gooleing and scowering forums all morning for this specific point.  Correct me if I'm wrong, but it appears sorcerer does not prevent the one point of permanent corruption from learning a spell in school or not.  Yet there are spells listed as being in the Sorcery school.  I'm trying to figure out why there even are sorcery spells when they are treated the same by the sorcerer as if they were from any other school.

On a related note, does it also cost more permanent corruption to buy an additional rank of a spell out of your school?

That is correct - sorcerers do not get a permanent corruption rebate for picking sorcerer based mystical powers.  I, as a GM, would expect the sorcerer to find a teacher for learning any mystical powers outside their tradition.  So, while the corruption cost is the same between sorcerer and other traditions, for a sorcerer, the availability is much harder.  A player will struggle to find the theurg/witch/ordo magic to teach someone willing to take corruption for their learning (not impossible, but hard).

It is correct that each rank in a mystical power costs you one point of permanent corruption, unless your tradition says otherwise.