Actually, this is pretty common in the advertising industry with US businesses. A large number of businesses depending on the industry have very diverse fiscal calendars that have different start dates and intervals. Most of the common fiscal calendar scripts out there do not help. I had to develop my own from a collection of others that fit my needs.

I think the reason why depends on the industry and depends on how you want to report on your spending/earnings. Controlling the time aspect of how you report those spending/earnings is a pretty critical piece. It's likely why there is no standard among everyone.