I would disagree with you on this comment Meir,
Such functionality exists in many editors EE has to compete against.
For example Sublime Text can swap lines with Ctrl-Shift-ArrowUp.
And it is one of its most used features: http://bit.ly/VYn8xW
Does it add slowness? I doubt that. Yet, people who shell $50 for an editor probably are on a 2-3 year hardware refresh cycle. For the rest, slowness is in each app.
On the contrary, it adds productivity.
Dragging is not going to do that in one hit, and for example not possible if you want to position a line at the top.
I think most EE users work on platforms as say Unix and use Windows as merely a window into their OS editing files quickly on the Win side. For them using keyboard is more natural and unintuitive than the mouse and they pick new commands naturally.