As far as the government is concerned, for individuals, the fiscal year is Jan. 1 to Dec. 31 and a lot of small corporations opt for those dates as well, just to make it easier I think to get all the tax work, etc. done at the same time. But when you incorporate, you have the option of deciding on a fiscal year that isn't based strictly on the typical calendar year. Lots of retailers in particular choose a fiscal period based on something other than year-end, if they expect to make a lot of holiday sales in December and will be facing returns from customers in January - makes it more complicated for accounting purposes.
And for a lot of companies, I think they just find it easier to not have to do a lot of accounting paperwork based on December when a lot of employees are out on vacation or holiday time.