I think technically all of Turkey falls into Europe according to Accor's mapping so you are right, being on the west or east side of the Strait probably does not change their contractual obligations. That said, because Turkey is "almost" Asia, according to your link above there are no fewer than 21 Accor hotels in Istanbul that (voluntarily?) decided to offer free breakfast nonetheless, and thankfully Raffles is one of them. I would guess they do so to remain competitive with other hotel chains.

However, Fairmont and Sofitel Taksim are notably missing from the list of properties offering free breakfast to Platinums and Diamonds.