It's the same situation with Mac OSX and is the same with ViewNX. Don't know why but I don't think is an issue of selecting a setting option. I use drag-and-drop to move photos from one folder to another but haven't tried it between directories.
>Thank you Preston for reminding me to drag and drop - for >some reason I had it in my head that drag and drop was doing a >'Copy' but yes it appears to be doing a 'Move' while within >ViewNX!
On the Mac, if you are dealing with source and destination folders that are on the same drive, drag and drop moves. If the source and destination are on different drives, D&D copies. If you want to force a copy where the system would normally just move files, hold down the Option key while dragging.
If you have a glitch before the Paste step has not been completed, it is possible to lose the images. With Copy you retain the original file in the orginal location and have to go back and delete it - but it ends up in the Recycle bin and can be recovered in the event of a problem.
I'm using Windows, but would expect the workflow impact to be similar with the Mac.