Basically -
You won't be asked to show the cc used to book on its website if you went through the extra security procedures eg Verify by Visa, Secure by Mastercard etc. If you cc has these features, you may even book the ticket for someone else. If you cancel your card before you travel, you need to keep the actual card and show IF requested. If you lost your card, you will need to get a letter from your bank stating the old card # and the new card # and the reason why you have a different card.
The only time you are asked to show the cc (and its not to swipe the card, but they will need it to verify the last four digits used only)... is if your cc does not have those features, and you did not go through the extra security protocol.
You will not need to show your cc if you booked through an OTA, or an actual travel agency.
SQ not the only airline doing this. Most airlines in Asia doing similar procedure.