"Apple should..." Ha! Apple, as a whole, doesn't care one whit about the way people used to buy Mac software. The App Store, both iOS and Mac, doesn't allow for any sort of nuanced models like timed trials, paid upgrades, package discounts, student discounts, etc. etc.

I think this is a overreaction to unregulated markets where merchants are constantly playing pricing games. As a consumer, it feels unfair when different people pay different prices depending on what hoops they've jumped through. However, Apple's approach feels unfair to me too, particularly the lack of trials and paid upgrades. I feel that this pushes everything towards "disposable" software rather than products that could grow over many revisions supported by upgrade from their users.