In blender at least you can specify the size of any primitive, measure the length of any edge, measure between any two points, move a vertice, object, or face by a specified amount etc. so this is just not true for blender at least. You can also annotate any dimension easily with a dynamically updating annotation. What you can't do easily (unless you're prepared to do some serious python scripting) is parametric / constraints based modelling because it's not a parametric modelling program. I'm not sure what else you'd want.

As to why visualisation folk don't care about dimensional accuracy, we do when necessary, but unless we're designing for 3d printing there's no point in worrying about things like clearances and tolerances since we're not making a physical object. Also, especially if we're doing arcvis, the demand is to knock out large quantities of models very quickly, not produce a perfect replica. I'm not going to worry about the exact dimensions of a piece of complex equipment or furniture I'm modelling if I need to produce a fully textured model in under an hour.