you are forgetting that most air compressors have moisture in them. some have lots of moisture (i try to drain mine every week at my home shop) . This is one reason tires filled with air increase in pressure. the moisture ! If you are seeing 10psi increases, you have a bunch of moisture in the air in the tires.. or are potentially under inflating them to begin with .
I have 2 trailers, both loaded are around 9000lb. One has air, i fill to about 72psi (e rated tires) and they go to about 77-78psi on a long haul. The xlr27 hs the nitro filled d rated tires, with fuel, bikes, water and even less psi to begin with, i don't see the same increase in psi. I'm not saying my example is the end all of the discussion, there is lots of info on nitro filling tires. I agree it isn't worth the time to find a nitro fill location, but to say it increases the same as a air from a big compressor that likely hasn't been drained of water in weeks is just wrong.
It is safe to say you won't be filling your tires with nitrogen ?