I've had the opposite experience. They have never failed to acknowledge warranty work, and it has happened more that a half-dozen times in three years.
I've only ever had one problem with warranty work - they refused to acknowledge "rust through" because the rust occurred where three pieces of metal were hemmed together, and only two had rusted through. So despite the fact that I could put a finger through two pieces of metal, the third one (they claimed) meant that the car hadn't rusted through and would not be covered.
Of course that was quite a few years ago.
What really has peeved me is the common defects they do have that they don't acknowledge...
I've actually had the least resistance from Ford of anyone. Not that they're angels, but they're a notch above Toyota when it comes to acknowledging mistakes, in my experience... Doesn't hurt either that the Taurus has been cheaper than the Camry (same miles, Taurus is 1 year older) by a few thousand $$$... And that gap just grew as the Camry just junked a CV joint.... There goes my Saturday.... %@#!#%!$#! :)