"Why is this new, what is E.P's point in posting it, and what message is he attempting to send out by posting it."

Maybe he is now realizing that surveying a planet with lots of spacecraft with high resolution camaras which is hit by most impactors per year can give us a fuller picture regarding impactors:
"The high-resolution cameras now circling Mars also are making further refinements possible, Hartmann said. The Mars Global Surveyor Camera detected about 20 new craters forming during a seven-year period of observations. "This was a tremendous advance," Hartmann said. "Now we can actually begin to measure how fast small craters are forming, how long it takes for a 10-meter-wide crater to form in a square mile, for instance." "