Some of them don't even start on a month boundary, or even on the same day every year. Cisco, for instance, has a fiscal year based on a retail calendar[0]; their fiscal year ends on the last full week in July.
("Honey I got you that Cisco 4500 you always wanted...")
Whereas for anything consumer e-commerce, you'd want a calendar with variable/sliding dates (e.g. SuperBowl) but that at least keeps the above events in the same quarter YoY, consistently.