It's all about keeping your brand name, front and center in the eyes of the public. If apple didn't release these pictures then the masses will start to think about other option ... and possibly purchase them instead.
By keeping up the illusion of new and innovated releases, apple keeps the mind of the people (?lemmings?) focused on themselves and not android or BB or windows 8. Lets face reality ... apple may have taken the lead out of the gate, but they have lost wind in the backstretch. The other phone makers have equaled and in many cases surpassed apple in quality, usability and design. If the enormous profit margins are to continue then you need to keep people using apple products. Luckily for apple, their marketing prowess has kept them ahead, but the masses are slowly educating themselves thus eroding apple's market share. To keep people interested, you need to tease them ... the pictures are a good start.
Seems like this would be too early for a model that would be debuting next fall. There are rumors about a spring release of a 5S, but that seems too quick. Not sure why they would release so soon for incremental improvements.
Given the T-mobile announcement and the ongoing negotiations with China Mobile, I think it would be more likely this is a different SKU of the 5 designed for one of those customers.