If they made that mistake, though, they'd likely complain that other weapons are like that too, since unless the weapon is so slow that it can't make more than one attack per second, the damage per second is generally considerably higher than the damage for one shot. I'd say the most likely cause is that they were using th Gauss rifle in VATS, though. I don't know the details, but I understand that the weapon is bugged in VATS, and does not do the damage it should. Alternately, they mean to say that the Gauss rifle is not as powerful as it should be, which I'd say is true for most energy weapons.
The DPS on the Gauss Rifle is accurate...
...assuming you ignore reload time. Which the DPS calculator does.
Grand Cookie: Ammo multipliers to damage (for over/max charge) are applied after DT. That's why it doesn't match up- your 70 damage MC plasma rifle against a 10 DT enemy is doing (40 - 10)*1.75, rather than (40*1.75)-10.