Thanks for the reply, Charlie. The link to the NED FAQ spells out all the detail on the vertical datum, including that in the conterminous US, all elevations are NAVD88 Meters, but some areas outside may be other datums. I verified this by checking some old scanned hardcopies of a USGS quad map and comparing the online streamed version from the ESRI mapping service.
It matched up being NAVD88 Meters. Your reply led to the answer.
I would think someone would want to edit the description on ther USA Topo service to include a description of the vertical datum and a link to the NED info, like you provided.