TBH he probably does them both for the same reason! The first time for no reason and the rest for superstition and/or mind games. I'm not saying that the leg out affects braking or corner speed but keeps the bike safer and more stable
He even manges to look impressive when he does it. My missus reckons its her favourite bit of the race but she bollocks at me if I do it infront of guests.
I don't watch much racing but I noticed this leg sticking out thing at the weekend. I thought it was because of all the rain and they wanted to give themselves a chance of keeping upright if the bike went out from under them during the corners (which did happen an on a number of occasions). I watch so little racing that I can't even tell you which course it was, all I know is that the race was stopped after 15 laps (I think) and that I was amazed how fast they still go even if it's throwing it down.