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


My Rogue RP-5 reverses polarity, so I switch the pos / neg at speaker terminals. The manual does not mention this, however, I wrote the company and they the amp does reverse the polarity. 

Now my question is...why? I would say 98% of buyers of this amp do not know to reverse the cable connections. I would say most reviewers did not as well. Yes, I realize, polarity reversal is not noticable in most instances. Especially, since many recordings are all over the place when it comes to polarity (at least that is what I've read).

So the question remains...why...why not just have the amp terminals set up so the buyer can just plug in as normal?
aberyclark
A question about the internal sonic effects in Al's theoretical 'some' preamps. Now if the actual electronics were creating the change. Then it would 'always' be one position which gave the apparent sort of signal. And the other position also would have a specific signal sound.  
So if the differences do not follow the switch, but rather follow the source polarity.. Then the suggested problem almarg discussed does not exist in the preamp in question.                     
If on the other hand it did follow the switch, then yeah your preamp polarity switch is messed up.   
I have several preamps into the main one. And one of them inverts. (Conrad Johnson ACT2) so with care adjusting the controls with  the same signal to several, I can switch the main preamp fro the Threshold FET TEN to the ACT 2. inverting with the selector switch, let alone the Bryston polarity switch. No matter how it is done. the results match.
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