It depends how you look at it. For some, they upgrade annually (Or they are enrolled to upgrade annually), so if they decide not to purchase the latest iPhone when it launches in September, then they clearly ‘skipped’ a whole year of _that_ generation iPhone.
One of the things that I love about the Apple iPhone Upgrade Program is that if you don't feel like upgrading a year later then you can just keep making payments and after two years you own the phone completely. It's a zero percent interest loan also.