Why do some manufacturers reverse preamp polarity in the first place?

Go play in the road.

All the sounds we hear are really nothing more than a series of compressions and rarefactions of air. Rapidly changing air pressure, in other words.

What causes the air to move like this in the first place? Strings, lips, drum skins, vocal chords. Squeaky chair. Tapping foot. 

Now this has gone on way too long already so here's the question: Compression or rarefaction: which comes first? Can't have polarity without a North and a South. Compression and rarefaction. So which comes first?

When you hit a drum, which way does the drum head move first? Down. Creates a vacuum above it. Rarefaction. Then, when it comes back up, compression. Most people would say the sound begins when the stick hits the skin. But that's down. That's rarefaction. Most people I would bet assume the sound begins with a pressure wave, not a rarefaction or vacuum. 

In other words polarity of sound does not exist. There was none to begin with, so there is none to be preserved, and none to be played back.

Yes folks it is that easy to reduce this whole conversation to the inanity that it is. Go play in the road is in this context as sensible a comment as any other.

That's the beauty of CD's, unlike digital files. If your CD is in reverse polarity, just play it upside down and the 0s become 1s and vice-versa.
Those of you who have traded in your CD players for media servers should feel pretty sheepish right about now.