Sounds like Apple is just letting Foxconn handle the 5S and Pegatron handles the 5C. Well, that makes sense. I don't see what the problem is. I wouldn't expect the 5C to sell as well as the 5S. Apple typically sells more of their top of the line models of iPhones as the older models ramp down in demand.
We will probably never know anything for sure, but it would be interesting to know if the 5c is selling proportionally the same compared to the 5s, as the 4s did to the 5.
Another thought: The 5s is traditionally to be a smaller upgrade to the 5, so that next year the 6 can be a breakout bigger step in advancement. With the fingerprint sensor, the 64 bit A7 CPU and the M7, the 5s is quite a step forward... then next year, the iPhone 6 ought to be awesome!!