I don't see it happening.
Most of the cost of HD game development is content creation, not programming. Once you've paid all those millions for the art, level design and voice work why freeze out a market of 20 million potential buyers to save a couple million dollars of programming cost? Those falling costs you describe will include falling porting costs, especially with licensed engines that work on both platforms.
If the platforms were more distinct then there would be game design compromises involved, but I just see far more incentive to port than I see not to.
"The worst part about these reviews is they are [subjective]--and their scores often depend on how drunk you got the media at a Street Fighter event." — Mona Hamilton, Capcom Senior VP of Marketing
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