I think everyone was wrong about the real reasons Apple wants the 5C. Everything you need to know about the 5C can be found on the slide where Apple listed the initial launch countries for the 5S. They made a big deal out of the fact that China is getting it on launch day. The way I see it, it's all about numbers and being able to pump out as many phones as quickly as possible. The cost of the device has got nothing to do with it.
They only way they're able to pull this off is because the equipment they use to create the metal chassis is being used 100% on the 5S. None of it is going to be used to produce last year's model. At the same time, it's incredibly easy to pump out millions upon millions of plastic chassis for the 5C for the markets where that extra $100 is enough to have a major impact on sales.