People who work on MRI machines use beryllium-copper tools (I know people in the business). That stuff makes stainless look cheap (just a quick google search, and it looks like an Ampco or Berylco BeCu hex key set runs about 3.5x the price of a Wera stainless set).
Plastic, aluminum, and wooden tools used to be used to make adjustments in TV's, because a steel screwdriver would affect the magnetic field, and alter the picture adjustment.
To the people who say that stainless can be made as strong as steel. Sure, some grades can outperform mild steel, but aside from in cryogenic and exceptionally corrosive environments (and extremes like that), there are plenty of readily available steels that will way outperform the best available stainless, and do it much cheaper.
I know this is called for in the construction of stainless building facades, and would expect it to be used on stainless turbine parts too.
Oh, and yes, non-magnetic stainless is austenitic, which is the soft variety, and is really unsuitable for tool use. Unfortunately, austenitic stainless is the kind that is most resistant to corrosion, so magnetic stainless suitable for tools is more likely to rust.
Stainless does have one place where it is important.
People working with stainless parts, often choose to use stainless tools to prevent corrosion. Simple contact between a stainless part and an ordinary steel tool can start the corrosion process in some cases. If your tools are stainless, you don't have this problem.