I havent read the other posts as im in a rush BUT:
I think timed obsolescence came about as after the boom of the 1920’s, when products were made to last at a high standard and everyone had money to spend (much of these products survive to day actually) the problem arose in the late 1920’s that no one needed to purchase new vaccuum cleaners etc. as they all already had one – so businesses went bust and it contributed to the great depression of the late 20’s early 30’s (until public work schemes and WW2 got the economy rolling again.. funny how war = profit). That’s what i was taught anyway, but yeah i’d say most companies make their products to break after x amount of years/use