I think you're in agreement with me, but the difference for the pro versions are usually substantial, such as weather proofing and more rugged materials (metal vs plastic) and usually more glass (less distortion at extremes, etc.). The market kinda makes sense: if you care about a few extra stops, and distortion at the extremes, then you are probably an enthusiast or professional who is willing to shell out. Otherwise, you'll have a great deal of fun with the cheap lenses.