Ok the transformation of objects works like this (moving). The matrix of parent object wich contains the parents position is added to the childs movement in parent space wich means you could move an group iwth a ball bouncing inside and this would move tha ball also but the bell would bounce.
but if you need something to be constrained to something moving it can also be done rivet mel works for polys but many very effective options do exsist!
what costrain does it takes some data and tranfeers it into the trensform of your object.
the concept is pretty important to understand since it makes animating stuff easier.