And the IK Spine makes posing much esier. AFAIK AM2001 spine is just a simple FK spine.
It's great that A:M is powerful enough that most novices can put a rig of some sort in by following a tutorial, and if someone has great new ideas for rigging A:M is a perfect laboratory for them. But TSM is about getting you past simple rigging and into real animating ASAP. All the things you learn about rigging while rigging really shed no light on how to animate well, so for me, the less time spent rigging, the better.
And just to elaborate on why this is handy...
suppose you've made a character and rigged him. then you decide you want to make a variation of the character with longer legs and a shorter torso. Stretching the mesh... not too hard, but adjusting the completed rig into that stretched mesh... huge hassle.
Much easier to adjust the basic skeleton bones and run TSM on them to properly put in all the invisible control bones that you'd have to srot through and rescale in a fully rigged model.
And suppose you decide to change the smartskin on a joint. It's easy to go back to your basic skeleton model (where you were supposed to do the smartskin anyway) then rerun TSM on it. You can adjust smartskin on a fully rigged model, but most people get confused and mess it up.