Well, I'll give you points for being observant and thorough!
I think ... (siren sounds, and a robot voice warns 'Danger! Will Robinson! Danger!) ... the ignorance and confusion on the hood issue is quite deliberate.
Look at who sells the systems: the same folks who do sprinkler systems. In both instances, the manufacturers have done their utmost to force customers to use not only their complete systems, but also their design services. They went so far as to 'obsolete' a perfectly fine extinguishing agent in favor of a new one that, amazingly, requires a new system be installed.
These protected sales arrangements make it easy to pass off details of your system as 'code requirements,' when such is not the case. Far too often, the 'expertise' of the installer is limited to just one brand and model of equipment.
I have something of a unique insight into this topic; my first 'real' job was testing various fire and alarm related products for a testing lab. As such, I read an awful lot of the standards, test procedures, and understand the way the system works. There have been a few times where I've had to point out to various 'experts' that the very data and materials they're misunderstanding originated with .... ME! Or, at least, I was there when the data was generated.
On the electrical forums, we may fuss and cuss over code issues- but the other codes seem to get a free pass. I'm really disappointed at some of the ignorance I've seen among "experts."
