Okay, how many of you played MtG? Until about 4 or 5 years ago, there were 2 different types fast or immediate type actions. You had instants where first in, first out. Then you had interrupts, which countered other cards. last in first out. This caused all sorts of problems at tourneys. It was changed to simplify the game because it became a constant rules argument.
Now my view is an immediate action is like the speed of the mind to reflexively respond faster than a body to move. Now I know that there are other feats or things that use an immediate action like being able to take a 5 foot step. This isn't something that I want to argue, but the psionics is the power of the mind. The mind from a modern perspective is faster than the reflexes of the body.