In mass production every tenth of a penny pays if it pays. This is a cost benefit analysis and not just a cost analysis. If in the lifetime of the car, this part will fail then it will have to be replaced at great expense, $1,800 to $3,000. If that happens under warranty, that will cost Tesla a lot. If that happens out of warranty, that will cost the customer a lot and will cost Tesla a lot in customer good will.

I sure hope Tesla has figured this out for 3 and the Y. (It has. According to the FA, this has to do with MCUv1 Tesla Model S and Model X units up to 2018.)