Actually, it's more that the people who interview in September are given the same consideration as those who interview in January.
You're still competing for a limited number of interview slots, which are given out on a rolling basis even if acceptances are not. If you're complete in July, you're at the front of the pile. If you're complete in December, you're at the back of the pile, and interview slots may be gone by the time your application comes up. The rest are somewhere between.