While this is true on its face, any OA publisher worth their salt offers a fee waiver program, and the expection from Day 1 of OA has been that these costs should be baked into grant applications and funding requests. Many funding bodies and institutions take care of this for you, having OA funds and assistance to take care of OA fees and to help direct publishing scientists to non-predatory publishers (Elsevier in particular can charge obscene OA fees)and also pick up the tab.

As such, it is very unusual for a Submitting author to have to pay an OA charge.

COI statement: I used to work for an OA-only publisher, but have not been employed there for the last 2 years.