Much of what you wrote echo's what I've been taught in classes on professional modelling.  I would add that it also depends on what you are developing meshes for.

Game design is more likely to use tri's not just because they rasterize, but also because being low poly it is not always possible to make a mesh (including organic ones) out of pure quads, in fact its rarely possible.

Conversely in high poly organic meshes using tri's often indicates inexperience in laying down control paths early on, or just plain sloppiness.  But when I look at an organic mesh with tris, I try to understand what the purpose is.   That is, was it really necessary at that point or did the modeller fail to take the time to correct the mesh so that the tri would not be necessary.  It really bugs me when I see two tris adjcent in an organic mesh where they serve no purpose and deleting a single edge would have eliminated the issue.  That is usually a clear indication of just plain sloppiness.  The preference in high poly organic meshes is quads because they do subdivide smoothly and evenly, provide flow control and other issues important chiefly in high end organic modelling. 

In structural / architectural modelling tris and ngons are far more acceptable because generally there are no deformations, no need to worry with mesh stretching, etc.  Its a static object that doesn't "move" so the mesh need not be purely quads or purely tris.  However, architectural meshes should generally be lower poly (and the mix of quads, tris and ngons should be used to achieve that) because those same objects are more often background in a still render or animation and should not be using a lot of resources.  Save that for your main characters that will ultimately be the focus of any image or animation.