Point of the math (seeing is it completey went over your head) is that you'd be replacing buttons LONG before you'd be replacing the screen. By the time you replace the number of buttons that would fail (common to Yamaha's arrangers) over years of giggin would easily exceed the cost of a screen replacement.
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GEAR: Yamaha MOXF-6, Casio MZX-500, Roland Juno-Di, M-Audio Venom, Roland RS-70, Yamaha PSR S700, M-Audio Axiom Pro-61 (Midi Controller). SOFTWARE: Mixcraft-7, PowerTracks Pro Audio 2013, Beat Thang Virtual, Dimension Le.