I'm skeptical that a stepper motor would be able to support it's own weight and more without a gearbox. This is especially important for making serial manipulators. Also keep in mind that what they're aiming for here is repeatability so that researchers can easily compare their algorithms. That means using parts that don't vary too much and minimizing the amount of assembly researchers have to do. There are much cheaper knock off versions of these actuators, although they may not be as repeatable. At the very least they aren't as well documented.
This is more about repeatable experiments than particular movements.
Regarding the price, the actuators seem to be ~240USD. A good stepper motor with the appropriate feedback mechanism to make it suitable for servo-like control plus a modern stepper motor controller that is suited for the robotics context will likely not be (much) cheaper and you have to hack together the servo functionality, tune settings, etc. - which seems detrimental if the goal is repeatability accross teams. I'm not in the target audience for these robots either but from the perspective of robustness and repeatable research they don't look too shabby.
