Poser renders pixels. Graphics files like jpg and png store pixels. The amount of detail in an image is determined solely by those pixels.

DPI and print size determine scaling for printing. Nothing more, nothing less. For a given print size e.g. in inches, a higher DPI will give you more detail, but it does it by creating an image with a larger number of pixels. If you want an image that will print 8x10", a 72dpi image will have a pixel dimension of 576x720, and a 300dpi image will have a pixel dimension of 2400x3000. That 300dpi image will absolutely have more detail but it has that detail because there are more pixels.

If the number of pixels is correct, you can trivially change the DPI setting with no loss of detail -- by changing the print size while keeping the pixel dimensions the same. What you can't do is increase the DPI setting while keeping the print size the same, because that would require getting more pixels which means creating information that isn't there.

All that said, there is clearly a bug in Poser 12, that causes it to incorrectly denote the DPI setting in the exported file. And that should be fixed. If you've changed the units in the render dimensions window, it may be especially bad because you won't see that the pixel dimensions are wrong. The workaround until it is fixed is to set the pixel dimensions correctly for your requirements.