To be fair, those percentages I gave, I made up for that example. Though I'd imagine they are something close to that. But it depends on the chip, the market and the company selling them.
You design those percentage bands, generally to the size of the market you're aiming the chip tiers at. The silicon will be as good as they can get it generally, nobody wants to push bad products out. Recalls and returns probably cost more in the long term than failing more chips and suffering a worse yield.
However if only 0.5% of your customer base is interested in paying more money for a faster chip, you only cream off the top 0.5% of chips.
You design those percentage bands, generally to the size of the market you're aiming the chip tiers at. The silicon will be as good as they can get it generally, nobody wants to push bad products out. Recalls and returns probably cost more in the long term than failing more chips and suffering a worse yield.
However if only 0.5% of your customer base is interested in paying more money for a faster chip, you only cream off the top 0.5% of chips.