At first I didn't get your comment. When I think of tilt-shift, I think of a special lens that you use to offset parallel line convergence in architectural photos (which is really more the "shift" part). Then I realized you were talking about the artificial miniaturization effect you get by manipulating depth-of-field using the "shift" effect. HDRI does tend to visually flatten an image a bit, removing depth of field, whereas tilt-shift expands the apparent depth of field. So I get it. :)