Your spare would be your cell phone app.

I agree, it's not a feature. It's annoying.

I agree, but realistically the car is already locked when you lose your keys, assuming you lock your car when you leave it. An exception would be, say, dropping your keys down a storm drain after getting out and before walking away, but even this is becoming unusual as more cars have push-to-start and capacitive exterior touch areas such that your key is always in your pocket.