You make some valid points, Wingnuts.
I'd only note that:
1. Those CO spot detectors are nigh on useless, if more than 12 months old or contaminated with e.g. cleaning chemicals, and
2. SafeWork NSW says: "... Carbon monoxide has a workplace exposure standard of 30 ppm averaged over eight hours. However, short term exposures above this are permittable to 60 ppm where total exposure at this level is less than 60 minutes in an eight-hour shift; 100 ppm where total exposure at this level is less than 30 minutes in an eight-hour shift ...".
Would you be happy to fly for e.g. 3 hours in an aircraft with the PIC exposed continuously to 100ppm of CO? Not this little black duck... (I'm not asserting those were the actual durations/levels in this case.)