I had driven with my wife somewhere, dropped her off, then drove to another place. I was about to shut off the car, when I realized I didn't have the key. She had it in her purse. Sure a light on the dash came on as she left the car, right in the same place the seatbelt light comes on. There are enough lights and chimes in a car in almost each use that I'm numb to them. There are many scenarios that can separate the keyless key from the vehicle and allow it to drive away.
Many members whine about the cost of these trucks, yet want all these kinds of features. This feature likely adds hundreds to the retail bottom line.
Spurshot's post in Push-to-start & keyless entry: Has anyone added these features? was marked as the answer