Why are Inverted Colors considered an accessibility feature?

Why is it that, in most operating systems, the "Inverted Colors" display setting is considered an accessibility feature? Both Windows and OS X include this option so it seems to be a recognized feature and not a vendor-specific quirk.

I understand that some users are color-blind. This could possibly justify the Black & White, or grey-scale modes for developers wanting to be assured that the experience is cohesive for everyone. What I don't understand is how or why does inverting the display color help someone with any specific, visual impairment or dysfunction.

As a programmer that wants to understand the need so that I can develop better accessible software, what purpose does this feature serve to the end user who has some form of visual impairment?

UPDATE

I asked this question quite a while ago, however, it just dawned on me -- I think I am one of those individuals that this feature was designed for. I almost always try to keep the contrast reversed from the typical settings for my text displays. I hate white backgrounds with dark text! As a coder, all of my textual GUIs are black with green text. This isn't just a throwback to the old monochrome, green screen days. The pairing of the two colors is quite comfortable to my eyes. However, staring at too much black-on-white actually hurts my eyes from some form of eye strain.

I mention this in an update because the color inversion feature is not useful.. it's annoying! As someone who needs a good feature like this, it's a shame that all implementations that I have ever seen are just a poor attempt at solving a problem. I would hope that Apple, Microsoft and others have done their research but I'm guessing that might not be the case. Color inversion just feels like slapping a band-aid on a bigger problem.

Developers, if you want to help people who need such a feature as to prevent eye-strain, find ways to change the text and page background and not necessarily the entire display.