Whoops, I have no clue what I was thinking there...

The water extinguishers are stainless. The CO2 and ABC are just painted. (while painted, those cylinders really like to rust up if mositure is left in them

I would hope not If they failed the physical test, then he'll know about it when his tank doesn't hold any pressure.

Someone probably left the cylinders, or a company they service is chaning over to ABC dry chem. They look old, and most individuals want a new extinguisher. The cylinder may be in perfect condition, but since water extinguishers are very limited in their use they just aren't as marketable as the Dry Chems. The only real benefit a water extinguisher has, is that it is cheaper and easier to refill (just tap water under pressure) than a dry chem, and it cleans up easier after use.