the leg muscles are so enormous that shocking them has an anabolic effect on the entire body - so working them out is good for the rest of you.
And on a related note, the biceps and abs are both such tiny muscle groups that the body-wide effects you'll see from targeting them are pretty minimal. Also, any ab gains you make will be masked if you are carrying any abdominal fat.
The muscles you really want to focus on for maximum whole-body growth are the big ones: quads, hamstrings, glutes, lats, pecs, traps. Delts, triceps, biceps, and calves are distinctly smaller. (And btw: The triceps make up more of the upper arm mass than the biceps ... so for powerful-looking arms, don't neglect the triceps!)
I also second what's been said here about the importance of a solid diet, which I honestly think contributes as much to muscle growth as the actual lifting. Aim high -- what will seem ridiculously high -- on lean protein such as tuna, cottage cheese, whey protein shakes, fish, poultry, eggs, etc. Eating 5-6 small meals a day instead of 3 larger meals is a great way to boost your protein intake.
Good luck!
Steve