When I picture a ship being "disabled," I imagine it has been blown full of holes by an assault chaingun, melted by a plasma blast, or had its entire onboard computer and crew compartment obliterated by some sabot missiles that punched through a weak spot in its armor. In other words, an observer could tell that the hulk drifting through space was once a ship, but the structural damage is so catastrophic that it cannot possibly be repaired. The Starfarer universe is absolutely filled with nasty weapons capable of inflicting this kind of harm, so it wouldn't surprise me if most ships ended their lives this way. After a battle, the victorious commander can do little besides recover CPU cores full of credits and strip the hulks of any useful supplies before abandoning them to the infinite gulf of space.
When a burned-out wreck takes so much punishment that it breaks into thousands of tiny pieces or dies in a fiery explosion, it is "destroyed" -- the once-proud ship has been reduced to a cloud of shattered armor plates and vaporized circuitry. This outcome is quite common for fighters, but anything larger than a frigate has to suffer a ludicrous amount of damage to be completely destroyed.
In very rare cases, the ship is rendered unfit for combat during the course of a battle but remains mostly intact. Perhaps the life support system was ruined, causing the deaths of 95% of the crew with little harm to the ship's hull. These are the special cases that get the "board or salvage" option after the battle. If the marines can clear the ship successfully, surplus crew from the player's fleet can make repair it and make it combat-ready within the week.
