When using line copy paste, the contents are inserted on the line above regardless of your cursor position. This makes it a simple way to move a line.

I regularly use cut without a selection as the most convenient way to delete a line, blank or not. It's faster than selecting and deleting. Copy less so (on a blank line) but it's consistent with cut. I use copy on non blank lines a lot though. As for the Shift+insert etc keys, I believe their longevity is linked to their utility for left handers (use the left hand for the mouse). Despite using them back in the DOS days, I really burnt their use in to my brain when I had to swap my mouse hand.