Almost all the exterior bolts in my Tiger's engine are SS, all factory original.
In your example they're not talking about fixings, more like actual parts of differing materials next to each other. Eg. I seem to recall that old model Land Rovers had problems cos they used ally and steel chassis/body parts fixed to each other and the ally parts rotted cos of galvanic corrosion.
Re-read the 'exceptions' 2nd paragraph bit about anode and cathode relative sizes. Our engines are a large block of alloy with small SS fixings - this is a 'good' way round in terms of reducing galvanic effects, add a touch of lubricant to the threads (i use waxoyl) and you minimise the risk further (as mentioned in article).