"Do you really think that you are going to get another contract if the customer states "it was cheap enough, too bad it blows up on a regular basis""

When you look at how frequently the various so-called ECUs in modern cars fail or require firmware upgrades it seems as though the car manufacturers couldn't care less - if anything they like it as it keeps the franchised dealers happy by giving them more work.

This whole question seems a bit meaningless anyway - the more you spend improving reliability the more reliable something will be (assuming the designer to be 100% competent). Naturally you can never actually reach 100% reliability so all you are left with is a sliding scale on which you have to draw the line. I would imagine cost is usually the deciding factor. After all, if your kit is so expensive you never sell anything then you'd do better selling less reliable stuff and accepting you will lose some repeat business.