You learn something new every day!

A scan of the RS catalogue shows you can get inexpensive devices using Darlington output stages with CTR values as high as 50 and more if you have the luxury of designing the circuit yourself, though they have a higher sturated output voltage. Problem is we're often dealing with couplers already installed in larger devices and cannot choose.

Pull-up/down resistors are often already included in many devices, it being a very bad idea to leave logic inputs to float as the mood takes them. This is how the common "enabled if left unconnected" principle is implemented.