Lefties tend to look odd when writing because they must curl there hand around to enable them to write with the letters slanted in the proper direction.
Sure! Blame it on the South!
Not me! (But I mostly print/write and there is no slant)
One big problem for lefties is that you're always pushing the pen into the paper. Pens, or pencils work a lot smoother if they're pulled across the page — as right-handers do. Obama’s twisted-hand grip is one way to partially overcome that problem. Awkward looking as it is, it allows a leftie to pull, rather than push, the pen across the page.
I learned to write cursive with fountain pens — where the big problem was not smearing the fresh ink all over the page. Also, fountain pens are much worse than ball points; to push across the page.
Some lefties go so far as to write from the bottom-right of the page, up to the top left of the page. They then rotate the page, to have the text facing the usual way. Of course, this requires that you write upside-down and backwards.
Also, lefties have to keep their hands from rubbing across the writing. Ink takes a little time to dry, so by curling the hand like that, it keeps the heel of the hand from rubbing the ink and smudging it.