You're overthinking this steamer purchase IMO. VX5000 has a proven track record as a commercial steamer. Why risk something else if that's in your budget?
to answer your question, my guess is there the just a variance in how they rate the machines. Steamers may put out 72psi initially but that pressure will drop once you start using it. More or less depending on how well the heating element can keep up. Cheaper steamers (your $200 and below ones) will advertise 50 or more psi, because they heat to that point, but their heating elements don't keep up well enough to maintain that pressure as steam is used. So it's easy to mislead consumers on pressure because it will give you that advertised pressure initially, then drop off within a few seconds of use. My guess is one giving that range of 65-72 is stating it will maintain 65psi but initially will give you 72psi until you start using it. Whoever makes the vx5000 may just be giving you an actual pressure rating while in use, which is a more accurate representation of how the machine will perform
