Given some of the recent posts about cable upgrades, I wonder if you notice that the "larger" the system, the more apparent the difference makes. For example, if you have small monitors in a small room vs. a large system such as a real four way speakers in a large area room, any upgrade such as cables will make more of a difference.
Let's take this analogy. If you have two digital pictures with different resolution, says one is 0.3 megapixel and one is 7megapixel, and zoom them on to two large computer screens, the difference in quality will be very apparent and the 7megapixel will have superior picture quality vs. the .3megapixel. But now if you display these two same pictures on very small computer monitors, the difference is not quite apparent and it is related to the picture resolution.
Now back to audio system, the larger the system will expose the quality of the equipment better because the sound will have to be projected in a larger air volume vs. a small systems. The difference will be amplified in a large system in similar way with pictures. I think that's why different people will perceive the same set component differently and some say the difference is significant while others may say the difference is minimal. From personal experience, I used to have a small system in a small room and it was hard for me to tell the difference, but now I have a much larger living room and much more high end system and any differences from different components are very easy to tell. Not only that, any difference when the system not fully warmed up is also very easily to tell.
Of course we have to consider the affects of "subjectivity", but what I said above plays a significant roll in how the sound is perceived.