It depends on what mobo, certain manufacturers supply a certain number of cables with certain mobos (e.g. my mobo came with 4 SATA cables and 2 E-SATA cables, etc). Cob is of course correct, with OEM hard drives (and OEM optical drives) no cables are supplied. However, with retail hard drives (and retail optical drives) cables are usually supplied.
If you were interested in anything specific, you could have course ask again and someone who has purchased the particular mobo (or drive) may enlighten you. Then again you could always send OCUK a webnote.