I think it is even simpler than that: The big companies that have thousands of customers doing millions of dollars of business on hundreds of thousands of machines need more time to patch because their is much more money / business to be lost. Not giving large companies time to patch would do more harm than good in the end.
It is fundamentally unfair, and is perfectly reasonable.
It is fundamentally unfair, and sets up a non-level playing field.
(inb4 "critical infrastructure")