It is logical that for a prey species, like the horse, efficient movement is one of THE fundamentals of survival so having hooves which can adapt to facilitate the best possible movement is a great evolutionary advantage.
Equally, if feet become unbalanced and horses aren't able to balance through their hooves then in some cases they change their limb flight in order to try and compensate.
I've blogged before about Ruby, who has now been here nearly 12 weeks. I posted an early update on how her landing was changing here - http://rockleyfarm.blogspot.co.uk/2013/04/undoing-twist.html - and she was already straightening up but after another 6 weeks the further improvement is clear to see.
The full footage is below but her movement is both straighter and has a more pronounced heel first landing.
I hope you can see from these photos nearly 12 weeks apart that her frog has re-orientated slightly - its a subtle shift but its been enough to allow her straighter movement. Ignore the asymmetric hoof shape - she is growing out old hoof wall and has "old" hoof capsule at ground level which looks odd. It should look much better in a few more weeks!
Ruby's feather makes it hard to see the angle changes clearly but there is a band of new growth which is better connected and no longer has the rings which she had in the old capsule.