Wikipedia is correct: on SD cards, you have to trust the host system (whatever the card is plugged in to) to honor the physical write protect switch. Here is the relevant text from the publicly available specification documents. Emphasis is mine.
SD Specifications Part 1
Version 4.10 January 22, 2013
4.3.6 Write Protect Management
Three write protect methods are supported in the SD Memory Card as follows:
- Mechanical write protect switch (Host responsibility only)
- Card internal write protect (Card's responsibility)
- Password protection card lock operation.
Mechanical Write Protect Switch
A mechanical sliding tablet on the
side of the card (refer to the Part 1 Standard Size SD Card Mechanical
Addendum) will be used by the user to indicate that a given card is
write protected or not. If the sliding tablet is positioned in such a
way that the window is open it means that the card is write protected.
If the window is close the card is not write-protected. A proper,
matched, switch on the socket side will indicate to the host that the
card is write-protected or not. It is the responsibility of the host
to protect the card. The position of the write protect switch is
unknown to the internal circuitry of the card.