9To5Mac comments saying, "Presumably, the slower SSD is a cheaper component for Apple to pack into the machine and helped the company achieve the $100 price drop, and even more aggressive education pricing for students."
I think that this is probably the best thing that Apple could have done in order to cut costs. Doing anything else, like downgrading the processor would not have gone over well. College students are slowly needing more and more computing power just for their school work and a slower processor would not have helped. By simply getting a slower SSD most people will not notice the difference as storage speeds are not a problem for many use cases as they are already plenty fast SSDs.