Instead of turning off the ignition with the clutch disengaged, if a person makes a habit of stopping their car by stalling the engine (leaving the transmission in gear and taking their foot off the clutch), will this cause any damage or excessive wear?
Using the clutch engagement to turn the vehicle off can definitely hurt the car.
Essentially what you're doing is wearing the clutch, bearings that lie within the motor, rings and valve seals. If you can visualize the physics and mechanics of what you're doing, it makes sense. When you let your foot off of the clutch pedal, you're pressing the friction disk to the flywheel. When this occurs the engine with the right amount of torque and RPM, will move the vehicle. If you let your foot off of the gas at idle you're stressing the inner workings of the engine.
The idea is that enough pre-loaded momentum (Revs) will allow you to move forward without damaging the engine. It's similar to the idea of power lifters when they "YANK" the weights rather than slowly lifting them. They use the momentum and velocity of their own body weight to pull the weight. An engine is very similar. This is why driving with a lightweight flywheel can be a bit tricky.
Excessive wear with occur most likely at the flywheel and friction disk in the clutch assembly. As you let your foot off the clutch it will experience a lot of heat and friction. If this is done everyday, it will wear out very quickly. You can also warp the flywheel if it's already hot. Not likely, but it's a possibility.
The connecting rod bearings will also have added stress when you do this. When you stall the car, the rod bearings get pushed up against the crank shaft and piston rods. Often times it's a jerking motion which is not healthy movement for a mechanism of that sort. It's very un-chronologically sound movement for a bearing of that type at a low RPM.
Piston rings can wear from this is well. The oil for your pan, and any oil squirt pumps that spray at the bottom of the piston will not be pumping sufficiently. This will wear out the cylinder wall and the piston rings over time.
Valve seals will be effected as well. When you stall the car like that, for the two or three seconds that it takes the car to die you will not have fuel or spark. You will leave unburnt fuel inside the cylinder. Additionally as the vehicle dies, the added air and fuel that did not combust will cause the cylinder to exceed pressure it wasn't designed to handle. This isn't really a problem if you do it every once in a while, but if you do it constantly problems can arise.