Yeah, that's what's great about the TRX, you got to train your body how you want to use it. Very few sports will use just one muscle group, and on the battlefield and outside of the sports arena you need to use your whole body, so why not train your whole body?
At the gym there were loads of guys with great upperbodies, but terrible legs and cores. The beauty of the TRX is that even the bicep curl isn't an isolation exercise, you still have to have core and leg stability.
Max