I'm just the Answer Geek, Dave, not a trained psychologist, so let me just say right up front that I have no way to answer your second question with any certainty. I'm happy to report, however, that your powers of observation seem to be pretty much intact. Because, yes, it's true that some CDs are louder than others. And it doesn't matter whether you play them through your PC, on your CD changer or in the car. As you probably remember from junior high school, sound is vibration transmitted through the air in the form of waves.
Sound waves are inherently analog.
CDs are digital. To put music onto a CD, sound must be converted from an analog wave into a stream of numbers. This process is called sampling. If you had your choice of listening to a recording that was sampled at a rate of 100 times per second on a scale that included 100 gradations or one that was sampled 500 times per second with 500 gradations, you'd naturally pick the latter because it offers a much more precise rendition of the original sound wave. The issue for recording engineers is to make sure they don't run out of numbers when they get to the top of the scale.