John, yes that is interesting and the handling of it doesn't appear to be consistent. My view would be that since 1 watt is a specific amount of power and 2.83 volts a specific voltage, that when Axiom uses 1 watt in its specs rather than 2.83 volts, it means exactly that. Therefore the spec would be an efficiency(rather than sensitivity) rating, e.g. the M80s would put out an SPL of 91dB at 1 meter with 1 watt of input. Since 1 acoustic watt at 1 meter is equivalent to about 112dB, 91dB at that distance would be an efficiency of just under 1%.
Since power equals volts(squared)divided by resistance, the two measurements would give the same dB number at 8ohms, i.e. 2.83 volts(squared)divided by 8ohms equals 1 watt. But 2.83 volts into 4ohms would give 2 watts. So, yes, if the spec is to be taken literally, the measurement into 4ohms is taken by turning the voltage down to 2 volts rather than 2.83, so that 1 watt of power is used.
