Okay, first off, I have to agree that the drawings aren't showing much talent, because they are just copies of poses that the DBZ characters already do. Like in most advertisements and merchandise, that is the stance they use... that one, and goku putting his hands together for a ki blast.
Now that I've said that, I will move on to the anatomical part. Okay, DBZ isn't really that great of a show to learn how to draw anatomy. (unless you want to draw a bunch of beefy guys) Although I guess the female bodies are decent enough to use as guides. The heads and hair and whatnot are purposely larger for the style, so you can't really complain that it's badly drawn.
If you want to learn anatomy, there are plenty of other anime shows with better bodies. Pretty much anything I've watched recently had decent body drawings. Stuff like Naruto, where the bodies are rather detailed, and it shows all sorts of action poses. I think it would be better to base drawings off of more realistic shows though, like Prince of Tennis. As the characters in the show usually dress in shorts, tennis shoes, and a shirt, and they have all different styles of clothing and stuff, and the bodies are in good proportion.
They also have more modern styles for shoes, pants, hats, etc, and again, many different poses. You can even find sketches of the people on the official site I think.
