Why do psolids and 3D moulding plines reference ground level?

[Sledge]

Hi all,

I've been wondering for awhile (and also whether this is a stupid question) , but why is it that when creating a psolid or moulding polyline it's reference height is relative to ground level. Eg, if I want to create a solid on a 2nd floor level (say for wall tiles) I have to add the height of the lower floor, (plus floor system) to place it correctly. IAE, if I have created a 3D moulding polyline halfway up a wall, why is it that when you click on the moulding in 3D view, it actually shows the selected line at ground level?