If the supplied cord has "properly" sized power conductors (for the 40-amp circuit), the power (IxIxR) losses in the cord, though certainly measurable, should be fairly insignificant.
Most installations will have cords much shorter than 50 feet, I suspect. I have no answer yet (from AV) on what the "available" cord lengths will be. I would guess that 15 to 25 feet would be more typical.
However, there are limited-access cases, like mine, where at least 30 feet will be needed, and 50 feet would help.
Also, the cable might be detachable from the home-version of the EVSE box (as a simple way of meeting the strain-relief safety requirement on the EVSE), so a short cord might be supplied for "typical" use, with the option to buy an "expensive" interchangeable longer cord.
See SOC/GID-Meter and CAN-Do Info
2011 LEAF, sold in 2015
2010 Prius, 2014 silver Tesla S
Nissan EVSE, mod to 240/120v 16A
Solar PV: 33 x 225W -> 7 kW max AC
To Sell: X-treme 5000Li EV motorcycle