It seems plausible. Less common sizes have a lower chance of being sold out, so if they can no longer be destroyed at the end and need to be further managed at lower quantities, it can become more cost effective to simply not make them. Whether it is true or not, I don't know.
Companies should have extensive data on how many of what size they can expect to sell.
Hmm... say you estimate that you will sell 1000 items of "normal size", you stock 1000 items, and hope that you sell all of them. You end up selling 900, you have a remaining 10%.
No say you estimate that you will sell 10 items of "less common size", you stock 10 items, and hope that you sell all of them. You end up selling 9, you have a remaining 10%.
How does that make a difference?