Why are my .dng files more grainy/noisy than .nef?

[JAHerrick]

I always convert my Nikon .NEF files to .DNG to work with them in Lightroom, but this week I opened some of the .NEF files in Nikon View NX2 and noticed they looked less grainy than their own .DNG counterparts. The .NEF file had some grain, which is to be expected, but the .DNG had noticeably more.

I was told that .DNG conversion was a lossless process, so I was surprised to find ANY difference between the two files. I also noticed some (relatively small, but non-zero) differences between their histograms. Why would there be ANY differences at all in the NEF-->DNG conversion process? Is it not really lossless? Is there something wrong with my settings?

I'm using a Mac OSX 10.8.4 (Mountain Lion), Nikon D5100 camera, Nikon View NX2 ver.2.7.6, , and Lightroom 4.4 with Camera raw 7.4.
Sample Images: https://www.dropbox.com/sh/vozpmbppxgsmh6r/LwohZnP327

Thank you for any insight you can provide

 

[480sparky]

Perhaps ViewNX applies the in-camera NR settings, while LR doesn't.

 

[KmH]

View NX2 and Lightroom use different algorithms to render Raw files.

The same applies for all different Raw converters.

Lightroom does zero noise reduction during raw file conversion. One of the reasons for using .DNG is that Nikon's .NEF file is an undocumented file type whose exact, proprietary specifications are known only to Nikon.

Your D5100 produces Raw files that have been compressed.