Here it is, hard evidence (sorry, pun absolutely intended) that termites DO eat hardwood timbers under certain situations. While it is true that certain timbers are considered "Termite Resistant", timber is never a consistent product and so sometimes we see termites infesting timber of all different types, sometimes even "Treated Pine". Its definitely a better option to use "Termite Resistant" timber for construction, but it is still important to discourage termite attack by minimizing external risk factors such as poor drainage and high soil levels.
The piece of hardwood pictured was in direct contact with the ground and was in constant contact with very damp soil from poor drainage under a home. These avoidable factors contributed to the termite infestation.