There are no abrasives in ATF, per se. There are friction modifiers in there that are are designed to alter the relationship between static and dynamic coeffecieints of friction (they are mostly derived from animal products) but it's not like lapping compound or anything. That being said, there is no set formula for say, Dextron III. There is a battery of tests and characteristics that the fluid needs to meet and if your fluid passes all of them you can call it Dextron (providing you pay a licensing fee to Afton Chemical).
But on to the subject at hand...
I too have heard of the method Tony described working. My theory is that it works mostly due to the fact that you are pouring an oil into the cylinders while firing and this frees-up stuck rings. I'm thinking the additives in the ATF don't really come into play all that much and that people use ATF to do this simply because it is a readily available, low viscosity
oil...and maybe it burns better (and cleaner) than motor oil.