I think the original thinking by Motorola was that the price point would remain fairly static (bar inflation, tax rises etc) and the specs would just improve as time went on.
Now it seems the specs are increasing, but so is the price - by quite a bit.
I do believe the Moto G is trying to move from where it was originally pitched, as a decent mid-range phone at a low-end price. When the Moto E came out, it enabled the price to creep up and now I wonder if Lenovo knows what it is doing.
You almost have the G series trying to take over the cheaper X series models (as the X becomes the Z) and the E series can take over where the G was, except I am not sure there will be another E series? Perhaps Lenovo plans to use its own name for the next lot of cheap phones?
The problem these days is that in such a saturated market, it seems crazy to launch a large portfolio of devices as against a few key ones. Low end, mid-range, high-end, done. Then release them every 12 months. At least MotoMaker allows some customisation, but three Moto G models? That seems silly.