An Apple cable has a much more robust 30-pin connector than cheaper non-Apple cables. The Apple connector has 2 plates soldered to the back of it - one on the top and another on the bottom. Cheaper connectors do not have these shielding plates.

An Apple cable comprises of: 1) 4 wires, 2) a strain relieving thread, 3) shielding mesh around the wires and strain relieving thread, 4) outer cover.