I'm guessing the plan to "feed off of Pennsylvania" was abandoned once they actually got into Pennsylvania, or the people of Gettysburg and surrounding farms were just better at refusing Confederate script. The suggestion that Lee planned to "feed off of Pennsylvania" was countered by his own statements that the area wasn't conducive to acquiring the necessary supplies his men and horses needed.
However, you make a point that I don't think has really been addressed before.... that Lee, upon arriving in Gettysburg, realized or was made-aware that the area wasn't good for provisioning his armies (and, no, I'm not being sarcastic with this). If that was in-fact the case then suddenly his logic and strategy makes a little more sense, even though I still don't agree with the decision to repeat the frontal assault on Day Three.