Hi Chuck,
I personally use "geographic coordinates" to mean latitude-longitude. Sometimes that could include ellipsoidal heights (heights/depths relative to the spheroid/ellipsoid surface).
I have seen others, including in Esri documentation, use "geographic coordinates" to mean the positions of a thing so the coordinates could be in a "geographic" or a "projected" coordinate system.
When Esri (and others) display data that's stored in latitude-longitude as a 2D map like in ArcMap, it usually using Plate Carree or pseudo-Plate Carree where the degrees of the latitude-longitude values are treated as if they're linear values. The regular Plate Carree projection just scales the degrees into meters--that is, the math of the projection is not complicated.
A graticule is a set of points or lines that show where the lines of latitude and longitude are in that map's projected coordinate system. So you actually have to convert the latitude-longitude into the map's coordinate system in order to place them properly.
If the display is truly 2D, then you can add 3D data to it, but usually not see the 3rd dimensional data except by querying a feature's properties. If you instead have a 2.5D or 3D display, then you can see the 3D properly placed and usually pan and tilt around it. It can get strange because much 3D GIS data is not using the same reference surface for the horizontal and vertical coordinate systems. That is, if the vertical coordinate system (VCS) is for orthometric/normal/geoidal/gravity-related/MSL/LLWS/etc., the "zero" surface for those is not the same as the projection surface of a PCS, nor a GCS's ellipsoidal surface. so that can cause some confusion.
Maybe that's why AutoCAD doesn't want to display latitude-longitude plus gravity-related heights/depths, but this is pure speculation on my part as I haven't used AutoCAD.
Melita