Preparing the surfaces to accept the adhesive is good practice. Usually on PVA you will see something like "Surfaces must be clean and dry". The oils in some woods would certainly violate this state. I have never bothered to pre-clean walnut although I have read that some do. Cherry, oaks, maples and other common domestics have never gotten special treatment out of me either. Goncals Alves is oily and waxy and I do wipe it with naphtha (acetone is fine, many evaporative cleaners will do). Bacote and some rosewoods are also on my list of woods getting a bit of attention before gluing. Generally I use exotics for detail work and not structural work but, epoxy or PVA, I still give them a quick wipe before gluing. YMMV.