YES, lots of them are not strong on their legs when first born. It takes days/weeks in some cases may take longer to straighten. I think if the foal is several months old and still showing signs of conformation incorrectness then I might ask questions, or simply pass on the foal until he matures. Some just take a while to "come together", especially the more refined ones.
There a lots of factors that can influence a foals development as well. Parents history of developement, proper feed, worming, farrier work, and I'm sure other things I can't think of right now.
Beth