I'll try another image of this car using the default blurry Iray HDRI for light and the modeled surroundings. This one used sun and sky lighting. I'll also try one with an ordinary format spherical image on a sphere as a light emitting texture.
This HDRI thing is starting to be silly. Thanks for the advice Rayman. However, it seems the work-arounds to make HDRI backgrounds useful is just going back to IBL or a sphere with a light emitting texture maybe plus a backdrop plane or other shape with an image. Since HDRI apparently doesn't work well without many troublesome work-arounds why use it? Here are my thoughts presented so I can be corrected and educated about HDRI.
-- I like the idea of IBL. The lighting puts the objects in the environment. The environment being a photo for realistic renders avoids detailed realistic modeling of things that aren't the main items. For instance, it would take much work to get my plants, wall, and ground to match the realism of the car. I'm not seeing an advantage to huge HDRI files nor their characteristics.
Claim: Lighting from an HDRI image is better.
-- The effect of brightness and color from different directions is present in regular IBL or light emitting sphere.
-- HDR images can represent very bright pixels and subtle variations of color. Thus "high dynamic range". Since normal humans can see about one million colors unless you are a tetrachromat (
link) you can't see these colors.
-- The ultra resolution of the images is not needed for lighting so the huge file size is wasted. HDRI enthusiast's own methods show that it is not needed since they sometimes produce or use "convolved" images which are intentionally blurry for lighting.
-- We don't have screens with a brightness that would blind you by looking at an HDR image of the sun so the extra brightness won't be seen. It could be that the extra brightness in HDRI's produces some subtle lighting difference in an ordinary dynamic range render but I doubt there is any significant improvement to a viewer's perception of the render.
Claim: HDRI is good for background environments.
-- Since the enormous files just produce blurry backgrounds while smaller normal format image files look great on a background sphere this is obviously not true. Why use a huge file when a smaller one works great?
-- I can see possible problems with non-super-resolution spherical images looking good at a distance but looking bad closer. I think that could happen for example under the car in this image. So work-arounds would be needed for non-HDRI too.
Claim: HDRI is good for reflections.
-- Blurry images are not good for reflections and only HDRI's of unimaginable size are clear.
-- Smaller normal format images look great on background spheres and thus in reflections. Why use a huge file when a smaller one works great?
High quality huge HDRI's are expensive or rare as free or cheap. Spherical (Mercator projection, typical sphere UV map) normal format images are more available. Rarity and expense means that illustrators would use fewer of them leading to monotony. "Oh not a car in THAT parking garage again."