Let’s take touchscreens for example. Apple doesn’t sell laptops with a touchscreen. Why? You suggested that it was because a touchscreen would threaten iPad sales.

I think that’s wrong and that the answer is simpler than that.

Apple doesn’t sell touchscreens because they want thin and light laptops. Touchscreens are heavy and thick. The math isn’t “adding a touchscreen will threaten iPad sales”. The math is “the market for a touchscreen laptop is smaller than the market for a super thin laptop”. Apple sells more laptops because they are super thin than they ever could if they added a touchscreen.

Why don’t they add a touchscreen as an option, you ask? Because they would need to have a different case to fit the touchscreen. And that would add more cost for not as much benefit.