not 100% sure, but are they just locators with attributes assigned to them? but just different shapes?

or are they like lattice deformers which deform the part of the body theyre attached to?

i believe the books say theyre not software specific, which means not nessecarily done in maya, i have seen those round things in MAX, theyre called gizmos, they function the same as locators (tho there are exceptions which i wont get into)

i mite b able to tell you how to do it (in maya), not the way they might mention in the book, but a way around it/similar to it if I knew what theyre used for