The old Courier magazine (much missed!) made a smart move when it adopted "Toby Barrett" measure in its reviews. Basically, all figures are measured from the top of the stand (or bottom of the feet) to the eye level. Figures may have headgear of various sizes, but almost all allow the eyes to see out*.
In addition to this, the figure was classed as light, medium or heavy for its bulk.
This standard at least made it easier to compare figures from various sources.
I agree that in a scaled size, such as 1/72, there is no reason that objects such as rifles should not always be the same size.
* some gladiator helms do not have eye slits, but that's Sparticus's problem.