Apart from the sneak attack damage that others have mentioned, rogues also get their turn more often (think of this as more attacks per round), further increasing a rogue's damage relative to the fighter. Also, as mentioned above, think of the fighter as a jack-of-all-trades of the martial craft - they can be unstoppable juggernauts wielding huge 2H weapons, archers plugging away from behind the lines, swashbucklers using dual-wield to make their enemies bleed, or an impregnable wall of a tank using a 1H and shield combo. The tank may be low on damage, but the others certainly won't. However, the common thread is that they will all generally be attacking head-on, and dealing slower but heavier hits than a rogue. Again, in D&D there are rules, exceptions to the rules, and exceptions to the exceptions, so take all of that with a grain of salt...