Re: HOw do I get my arms fuller and rounder looking?
I think there are several possible explanations:
1) You're not getting enough protein in your diet for your muscles to grow fully from the work you're doing. How much protein do you get a day? If you're a heavy weight trainer, you want 0.8-1gram per lb of bodyweight.
2) You're not doing the exercises with a full ROM (range of motion). For example, with standing barbell curls, you need to lower the weight fully so that your arms are almost straight (don't lock out though - you want to keep the tension on your bicep the entire set). If the weight is too heavy, you might find yourself only able to do partial reps, which are no good. Likewise don't 'jump' the weight up with your legs, this is just cheating.
3) Try some different exercises. Personally I prefer preacher curls to concentration curls. With preacher your are forced to work harder to get each rep, especially if you let the weight right down like you're supposed to. For triceps, I like tricep pushdowns with either a V-bar or a rope pull if you've got one. Also skullcrushers and pullovers are quite good.
Just a few possibilities. In general though I wouldn't try and compare yourself with other people too much - genetics does play a large part in what your muscles look like. I have a training partner who does exactly the same workouts as me, and yet his physique is quite different - he has bigger looking biceps and shoulders, I have bigger triceps and chest. Go figure...