I would like to know why in some Character riggs the body parts are completely separate? No modeled body part is connected to the other, the only thing binding the character is the rigg. How do they get the rigg to be smoothed out etc. when its time to render? Do they reconnect the parts and how?
Often times characters are created from segmented pieces because building a character from one piece of geometry can pose many challenges that simply breaking up the character and creating separate pieces will overcome. For instance, the arm might be created easily from polys, while the shirt may be easier to create using NURBS. In this case, you can either fight with NURBS to create the arm or fight with Polys to create the shirt, or you can skip all of that and just do whats best (and easiest) for the character by creating the arm with polys and the shirt with NURBS. This is often a very common approach to modeling characters.
Then each piece is assigned its place in the rig for animation. The seams are often times cleverly hidden behind other geometry (in this case the arm would go slightly up into the shirt) or the seams will be hidden at the texture seams. I know that with NURBS, stitching is sometimes a factor as well.
If the character is well planned, and the rig is built properly, the seams will never show up. One important aspect of this is to plan your character according to what you're going to have it do. For instance, if your character is only going to walk in a circle, then there's no reason to rig it up to do push-ups, Climb over walls, or eat a hamburger; that's too much work for no reward. So, the seams and the rig will both be planned out according to what the character will be doing.
Hope that helps.