(Strangely my first reply never seems to have made it on to the page)
'Very odd that scientists have supposedly ignored this.'
They've not ignored it, they didn't think there were significant changes in elevation on the Eastern Seaboard. The ES is considered a passive margin - that is it is effectively tectonically inert - it is not being actively rifted (like the Red Sea) and being extended; subducted and shortened (like the Pacific coast of South America); or sheared (like California). So geologists have previously treated the Mantle, which is at least 60km deep under the ES, as a rigid block in isostatic equilibrium. As such it was reasonable to assume high terraces and wave cut platforms were the result only of changes in sea level.
However, improved seismic techniques have allowed them to calculate the velocity of waves passing through the Upper Mantle and it is not behaving homogeneously, instead some parts under the ES appear to be less dense suggesting the Upper Mantle under a passive margin is not entirely rigid and may be convecting slowly. This is likely to have surface effects, so some of the wave cut platforms along the ES have been pushed up by deep processes and are not wholly due to higher sea levels.
What Lewis' article neglects to say is that the ES isn't the only evidence of high sea levels 3Mya in the World. It has been the benchmark (ahem) in the past because of its excellent exposure. But there are others. What will need to be done is to try and get a better estimate of the actual magnitude of the rise. This new knowledge has made that much harder.
What I find interesting as a geologist is that the ES gets infrequent massive earthquakes which are poorly understood. This might help clarify the situation somewhat.