the use of poe injectors is a mixed discussion, especially if you are using a sync injector like Packetflux. Plus the lower and wider voltage requirements is nice for sites that run off batteries. 802.3af/at all require power to not exceed 56v, but the charging voltage of a 48v battery can be as high as 62v during equalization whereas a 24v system has a 29v equalization.
This is all besides the fact that the radios use 5 and 12v internally regardless of the supply method. The higher supply voltage is to reduce the current over the wire and the devices have a converter to drop the voltage and thus increase the available current. Still have to keep below the max wattage of the wires though.