Well, look at it like this: would it be reasonable to express unhappiness about the standard cars if they were coded on the disk, taking up no resources at all, and were not visible in the game? I don't think anyone has a problem with them being in existence, that's just not really a sensible position no matter where you stand.
If the standard cars could be hidden, I agree completely. No need to express unhappiness. Those who don't enjoy them could simply disable them. I have no problem with a feature I don't like, if I know it can be disabled. However, it doesn't seem like that is going to be the case in GT6 because they're removing the distinction between premium and standard models. Maybe the standard cars will surprise me with their enhanced quality (if they are properly enhanced) and the removal of the separation will actually be justifiable, but we'll have to wait and see.
Well, they don't look anything like Minecraft objects in BF. MC gets to the point where it can be difficult to determine what an object is. Standard cars don't have that problem. GT4 was able to fool me into thinking I was watching real race footage at times. The models are still good enough for that.
I would also put physics far ahead of graphics when it comes to immersion personally. The most immersive game I've ever played was Falcon 4.0 with visible repeating terrain tiles and cardboard cutouts for enemy fighters compared to your high detail F-16 model.
This is going to vary from person to person though.
Like I said, the Battlefield 4 example was leaning towards the extreme, but it's the comparison I thought would best transmit my idea.
As stated by you at the end of your post, what is considered satisfactory regarding visual quality, varies from individual to individual. You are simply more forgiving than I am. I tend to approach anything I like with a perfectionist (within the skill level involved) point of view. This applies to what I do myself and to what others do that I appreciate. So after seeing what Polyphony is capable of with the premium cars, I was disappointed with the standard cars because I knew Polyphony was capable of much better.
With regards to physics being more important than graphics, I can agree with you to most extents. But here's the thing, it's not the overall quality of the graphics that is relevant to me, it's the consistency of the graphics. I still play and enjoy rFactor (the first one). I think the game has great physics and is very challenging. Graphically, even though I try to use high-quality add-ons, the game really doesn't reach the level of GT5 (when at its best). However, I made sure to choose add-ons of similar quality levels, making the visuals of the game, even though inferior to GT5, uniform across the board. That to me, just like physics, is what is important to keep me immersed.