It would certainly be a more positive sign if the route was to remain daily year round. Delta is also reducing its ATL route to 5 weekly for the winter season, so it will be interesting to see if US and EI reduce services more than previous winter's
According to EI there US flights done very well from DUB last winter so I don't see why they will cut.
IAD bookings are very good and the reduction is nothing to be worried about as all carriers reduce in low season. All US carriers are cutting for winter with DL and UA closing a number of major European routes because of rising fuel prices.