Pardon my ignorant question, but how is it a problem to have traction control? Wouldn't it be enough to glue traction strips to the feet or something?
That's like wearing shoes with golf spikes all the time.
Traction control for feet does roughly the same thing as automotive traction control for cars. The basic idea is to keep the sideways force below the break-loose point. This is the down force on the wheel times the coefficient of friction.
For car wheels, the down force is mostly constant. For a legged robot, it changes throughout the ground contact phase So the side force has to be actively controlled and changed throughout the ground contact. It's also necessary to compensate for leg angle.
Legs have an additional option. If a leg has three joints, you can adjust the angle at which the contact force is applied. This is a big win on hills.
I used to work on this stuff in the mid-1990s, but nobody was interested in building legged robots back then. It could be used for animation, but it was overkill for games. I never expected that DARPA would spend $120 million on BigDog. Robotics projects in the 1990s were tiny.