In this case the OP is talking about the RDU-EWR flight that is "known" to be delayed. I'm guessing that's a CoCo flight and those are the first to take a hit when EWR starts to back up, which is pretty much every single day of the year. Yes, CO schedules it that way because there are random days where it is on time or close enough that it doesn't matter. But those days are really few and far between.