I don't know if is people's fault or the software's fault not be a clean model. What I know is that most of downloaded 3ds meshes has this problem. I don't model with 3ds, Rhino has better results, but even with Rhino there is a lack of continuity between surfaces. You can increase the precision and this reduces the errors, but as result you have increased without any need the number of polygons and the errors still persist but are less visible. Is much better in a mesh of 400 faces to correct by hand 30 faces with a perfect mesh as result than to increase the precision and have a mesh of 2000 faces that looks good. The only decimator that I have used is the Polychop plugin for 3ds, is a free plugin and in some cases produce good results.

Stupidity also evolves!