There you go again PDR1, putting up another defense of what if they fail.
What if any commercially used bit of kit fails - the manufacturer can be sued.
Just to take hughes500's examples (and I have owned a 500)
500 switch $135. If it fails the item wont turn on or off
anaesthetic machine switch - far more complex $42. If it fails the patient dies
500 pressure switch $14500. Similar used for orthopaedic operations £160. Again if it fails patient ends up with failed joint replacement,permanent limp, pay out massive
Aviation is not the only industry where items are used on a small scale, have to be designed and tracked and where failure can result in horrendous litigation.