Non-destructive editing is a marketing term that means very little (in reality). ACR/LR are parametric editors that do not apply the settings until a rendered file is created...then the pixels are indeed modified. Are they destructed? Nope...just rendered.
Photoshop can also do a lot of parametric editing when it comes to adjustment layers...like ACR/LR, those edits are applied until flattened...better yet is the ability to use the ACR filter inside of Photoshop proper.
The only "destructive" editing I ever do is trash bad shots...everything else I do I do to an image is designed to improve the image, not degrade it.
Short of downsampling from 16-8 bit or taking a ProPhoto RGB image and converting it to sRGB, there's really nothing in ACR/LR or even Photoshop that is really "destructive", just edit with various sorts of consequences...
Now, if you want to change the term non-destructive editing to something like infinitely re-editable, I'm ok with that. I hated the term non-destructive from the moment I first heard it. It's just a buzzword that is ambiguous not really very useful.
Oh, the people on DPReview seem to like it...does that mean anything?
:~)