The big thing for me is I wouldn't want to be sitting on an air receiver with 40 bar (600 psi) in it. Thats a lot of stored energy should anything go wrong!

So is having 17 Litres of Super Unleaded under your face in the fuel tank.

I agree, but this has got both. Air receivers for vehicles (like Air brake tanks on trucks) have a different design code to one that you find in industry, to enable them to withstand crash damage. Anything that is pressurised whilst the vehcile is moving must be to that design code or it has to be de pressurised before the vehcile can move.
Air brake tanks generally have 8 to 10 bar in them and not 40!