This thread should really have had one of those poll things at the top, "Are you left, right, both or neither?"
I'm right handed, as is my younger brother, but both my parents are left handed. My left hand is useless for much except fork operation (only when used in conjunction with a knife of course, if I'm only using a fork to eat something like fried rice I just use my right hand), typing and anything that falls into "holding things"
Although, I can also write backwards with my left hand easier than it would be to try and persuade it to write in the correct direction.
Regarding creative skills, I'm useless at drawing (but then, I don't try very hard). I'm into software development though, which requires such skills in trying to work out how to make the computer do seemingly simple things
Maybe it's just a side-effect of the brain developing from conception that decides whether someone is left or right handed. That would sound quite likely to me, more so than the idea that jousting would be helped