You don't 'buy' an Oyster card (except Visitor Oyster cards). You pay a deposit to get the card, which is refunded if you surrender the card
Yes.
For those who have Oysters which are more than 10 years old, there may not be any deposit at all - no deposit was paid on Oysters that were loaded with a travelcard at the time of purchase, until around 2009.
Nowadays, it is simple and trivial to refund Oysters with a balance of £10 or less at most TfL ticket machines (ones which accept banknotes). It is also simple to check whether there is a deposit on the card (and the amount of the deposit, which may be £3 or £5) by beginning the refund process.
For anyone who is worried about needing to replace an Oyster, just use it until the balance is less than £10, refund it, and buy a new one at the same machine (all TfL machines now sell new Oysters). However, you will have to pay the £5 deposit even if your old card didn't have any deposit.
After refunding an Oyster, it is disabled. However, Oysters without a deposit can be reloaded and reused several times after refunding the balance. As an experiment, I attempted to refund the same Oyster (purchased in 2003), reload it and then pay for journeys, then refund it again multiple times. After the 20th refund, the card stopped working.
London is one of the rare cities which doesn't actually charge for its public transport card and allows cash refunds in full (although refunds of a balance greater than £10 require a UK bank account). The Netherlands example given is not really a fee to replace the card, it is a fee that must be paid every 5 years in order to use the card, and this is by design.