I am glad that the FP end time is not enforced and I hope they never change this. On more than one occasion I've been given a FP time that directly conflicts with my dining reservation.
I am not attacking you personally, but I do want to make this point: I think the way you approach FP is part of the problem. Before you got your FP, you could clearly see that the return time conflicted with your dining reservation. So, why would you still get the FP?
If I go to get a FP and I see that the return times conflict with a dining reservation, I DON'T go ahead and get the FP. I let OTHERS get the FP instead, because they can actually use it when I can't. I either go back later to get a later return time, I have to wait in the stand-by line, or wait til the next day (or next trip). I guess it is too much to expect the same sort of decency from others, especially at a place like WDW where most guests just want to take and take and take without any regard for the rest of us.
Having the end time enforced would make people think before they blindly accepted a FP, otherwise the FP system doesn't work as well as it should. Without the end time enforcement people will just take as many as they can, regardless of conflicts, thus taking it from those of us who would actually use it during the assigned hour window.