There are a dozen reasons why a 10btc Casascius was peeled; inherited, stolen, anonymity (not selling directly), fear of transporting high value, etc... The conundrum we all deal with here is the higher the value of BTC, the less premium we demand on our coins. Arguably the best time to sell a Casascius is when BTC $ value is low, thus receiving say 18-19BTC for a 10BTC back when we were in the $200-300 range. Now you'd be lucky to get 13BTC. I buy Casascius as a way to force myself to hodl and ultimately to hand them down to my kids, eventually all of mine will be peeled.
I'm not sure I agree about the best time to sell being when the BTC value is low. That's an odd game of "what if" and I think people would be wise to consider their entire portfolio and not place so much into the idea that when you sell something for BTC that BTC is somehow separate from your holdings and not a part of your managed portfolio. Everything should be considered traded at the USD value at the time of trade so you can gauge value over time. You don't consider your groceries cheaper when Bitcoin goes up because they would cost less BTC do you? Do you feel like your home is worth less when the value of Bitcoin goes up? Do you consider the housing market a scam because if you spent BTC on a house in 2011 then you 'lost' a ton of BTC? Personally, I don't think the stock market or housing market is a scam or not depending on what the Bitcoin exchange rate does, but so many in this community (incorrectly) think this way.
Regardless of the price of BTC at the time, I think users are better off selling one now for $100,000+ worth of BTC, then selling one in 2013 for $200 in BTC. If you don't think that is true, ask somebody who sold a 10 BTC Casascius coin back then if they would prefer to own the coin now. I know I don't regret spending BTC back then to get mine. One of the greatest investments of my lifetime, even if I did 'lose' BTC in the process.
I do agree with your final statement though. I wouldn't sell my pair of 10 BTC coins for less than $300,000 today and the more I see the market premiums disappear on these coins, the more likely I am to peel mine when the day comes as well.