You already answered yourself: this is because the principle of casualty does not prohibit such motion.
Tangential motion and moving away from another object with superluminal velocity is not prohibited because in such processes the casualty cannot brake. What is prohibited is approaching another object with superluminal velocity.
The only reason why we do not see objects moving away from each other at superluminal speeds is because moving from some object at v>c usually means approaching another object with v>c, and this is prohibited. But in the case of the expansion of Universe it is possible to move away from one object without approaching another, and that's why superluminal growth of distances between two galaxies separated by big distances is possible.
Even more, due to expansion of universe any light rays going from us (or any other atationary observer) have velocity somewhat greater than c and any light rays going toward us have velocity smaller than c. This of course means also that any two stationary observers move away from each other.
There is only one case where one can imagine superluminal approaching of two objects: when both are under the horizon of a black hole. When an object approaches a black hole, he reaches superluminal tangential velocity at ergosphere (which is outside the black hole horizon so the object can return) and the radial velocity reaches c exactly at the horizon. Mathematically this means that inside the horizon the object should have radial velocity greater than c. But this is not the case: once object reached c (or near c) at the horizon, the time stops for him and he remains there until the black hole explodes (finally evaporates).