This is not true at all.
First off you CAN clip dots, but it doesn't do the same DPCT, it does the same DPS. The difference being there is a dps increase in clipping your dot at the last possible second, but there is a DPS loss clipping it several gcds early. Lets say you clip your dots before the last tick, you can lose 2-3 seconds of dot time per early clip. So over the course of the fight you might cast lets say Unstable Affliction 12 times instead of the need 9-10. This effectively lowers the DPCT due to not getting the full duration and wasting gcds, however the DPS of dots is still going to be the same.
Second Channeled spells work the same as they always have; if you clip it you lose that tick. If you wan't to try it out go spam drain soul and watch yourself never get a tick.