The first 2 years I setup my 75G I was getting 0.00 readings on my $200 Hanna Phosphate meter... even went so far as to have a fellow reefer bring his same meter over to test to verify because no one could believe my system could have that reading. Since that time though it has been a constant battle as things have been skewed in my tank.
I don't agree that you can't remove more N than P or more P than N, that is easily proven to be false. Anyone can put a ton of GFO in a system that has high nitrates and phosphates and skew the parameters that way. That same thinking goes the other direction in terms of bacteria. Bacteria seem to either follow the redfield ratio closely OR they remove more nitrates than phosphates (in anaerobic areas), but as far as I know, there isn't a bacteria strain that consumes more phosphates than nitrates for our hobby (there are strains that are used for wastewater treatment that do consume more Phosphates than Nitrates), meaning if all things are equal, algae and bacteria, most systems will likely skew towards a phosphate problem over time because even in barebottom systems there are anaerobic areas within live rock for denitrification bacteria to colonize. This can happen fairly quickly (in reef terms, 2 years on my system) or can take decades, it all depends on the tank setup.
Your analogy of a sealed room is a little flawed. I can't even think of how that analogy applies here. To me, that analogy is more like saying "I have a 100G tank with 5.0 phosphates and 200 nitrates, but when I dump my entire 100G of dirty water into the ocean, it doesn't seem to have any effect on the parameters in the ocean". That is the same as removing just the O2 from a room, leaving CO2 and the other gasses, then opening a door. The sheer volume of "air" on the outside vs inside will quickly equalize the air inside when the door is opened... but I don't see how that relates to phosphates/nitrates and adding food to a system. If I have a system with .1 phosphates and 0 nitrates and by your thinking "everything is stalled until more food is added" then that just proves what I have been trying to say. When you add food to get things moving again, your adding food back into the system in the redfield ratio, or worse, slightly skewed towards more phosphates than the redfield ratio, then eventually those phosphates will continue to climb because every time the system "stalls" due to low nitrates, the phosphates will no longer lower. Basic math.. if your adding 2 phosphates a day and 1 nitrate, and you system consumes 1 phosphate and 1 nitrate a day, you will have a left over 1 phosphate when your done.. repeat this day after day and you can see how phosphates can become a problem over time.