That was the point I made.
Adding the pixel dimensions has the potential to create confusion and mislead as output for any crop ratio can be at any size.
An export doesn't have to be at the native file resolution and very often it's not what you want at all.
Perhaps Bob is too young (or old, or inexperienced) in printing in the darkroom of which Lightroom mimics. Consider its name Bob.
One shoots a 4x5 negative and makes a proof sheet. One can use cropping L's and a maker to crop the proof sheet, in no way have the cropped or rendered a print** at any size. Not until the neg is placed into an enlarger and the user decides the paper size, adjusts the enlarger and cropping and exposes the paper does the print get cropped. This is no different in Lightroom.
The idea that someone needs exact numbers of pixels
to crop equally makes zero sense to me. I was trained by some very good photographers (Jay Maisel being one) to crop based on the image itself, not on some arbitrary number. I can't fathom how to crop based on pixels and not the image itself and perhaps an aspect ratio although for me, image content is paramount. I don't see how cropping a print or an image to 8x10 exactly, or 8.25x10.25 or 8.22x10.22 is at all a means to affect a crop. Ditto with 1200x1600 or 1209x1609 or anything else for that matter.
If I want a rendered image at 1200x1600, I tell LR what I want and I get
exactly that number of pixels. And at the same time, I can get
any set of HxW pixels from the same image at the same time when I export in a batch.
This idea one needs to crop by pixels makes zero sense to me and apparently others including the Adobe teams. Certainly with a product that isn't a pixel editor. Photoshop is a pixel editor. Photoshop provides those controls.
Use the right tool for the right job after understanding how the tool works.
** as to rendering a print, maybe Bob will find this useful too:
http://www.lumita.com/site_media/work/whitepapers/files/pscs3_rendering_image.pdf