They can crank out rebel after rebel after rebel because for key components they're just drawing from their existing parts bin and forking software projects, with minor tweaks so development and QA efforts are minimal, and offer a huge return for minimal investment. For the XD line (and the XXD) it's a different matter, since those models usually get the sensors, software, and other bleeding-edge components first. That's also why the xD and xxD models cost so much initially - the first unit to roll off the assembly line cost tens to hundreds of millions of dollars to product - the second about half as much, and so on until R&D is fully amortized, enabling Canon (and Nikon) to lower the price, as the sales morph from recovering losses to earning profits. See: amortization.
You're either oversimplyfing or you dont know what you're talking about;
First off there aren't really any "bleeding edge components" in XD or XXD lines, at least not "edgier" than a touch screen or that 70d sensor etc, yes usually tech trickles down the line but given the yearly cycle of XXXD series its bound to introduce "edgy" stuff on its own.
It's one thing to add a gimmicky articulated screen to a low-end camera body using screens from your parts bin and make a new plastic mold, and tweak sensor designs you borrowed from pro and semi-pro cameras and get the product out in a month or three, and quite another to develop a whole new hardware and software architecture (as well as a fab process, metal casting molds and precision machining tooling with a tolerance of a few microns for a mass-produced product) from the ground up.
I dont really know where to start with this one.., it contains some truth in that yes developing a whole new hardware and software architecture is more time consuming than incorporating an articulated screen but then again it never happens to develop a new hardware and software architecture for a product such as XD; there also tech tricles down from the FF models, and what new there is isnt enough to warrant the "whole new" title. Plus last i remember IM tooling is about the same as mag tooling plus its actually absurd claiming a tolerance of a few microns for a mass-produced product, where on earth you saw something on a dslr chassis requiring more than die casting tolerances for mag alloy?