Why is this the exclusive domain of "IP/IT/IS"?
In old school western physical culture, tendon strength or sinewy strength were commonly referred to. These elements have not been lost in arts such as wrestling, weight lifting, and gymnastics.
Never said it was, wiry builds are found elsewhere, though you may find people who have thick and wiry feet, but more normal looking bodies.
In order to condition your feet, you have to train so that your feet get very heavy. That is to say that after a few minutes, your feet will hurt due to the pressure. This thickening indicates that a lot of weight/loading is transfered into the feet. One might think that they always have a lot of weight going into the feet, but that isn't always the case. Lets discuss how to do that in some aikido exercises.
Doing warmups is a great time to work on this, so is funakogi undo. In funakogi undo, when you drive your hips, you don't just want that motion to go forwards. Doing so makes the rear foot get light. You need to keep both feet heavy as you perform the motion. Part of that is how you drive the hips forward and back and how you involve the lower back. When driving the hips forward, the motion to drive the lower hips forward doesn't mean that you roll the hips forward with the lower back.
If you do, you will find that drives the motion upwards and makes the rear foot light. Also, I find that leaves my lower back fatigued rather than the hips. Instead drive them forwards by opening the hips. You will feel your legs want to open up too, but don't let them.
When performing aikiken or working on suburi, when you swing, you want your feet to get very heavy. That is to say when you swing, the weight and corresponding pressure in your feet should increase as you bring the sword downwards. If it doesn't, it indicates that your energy is going out rather than down, which means your weight is going forwards and your feet will feel lighter. Thus even when receiving a cut with your bokken during kata, the recieved energy will mostly go into the arms or maybe the upper torso, rather than reflecting off the floor. You do not want to stomp the foot into the ground; obviously that can injure the foot, but its not at all what I am referring to as causing pain in the feet :P