Sports injuries mostly bad luck and a player's risk threshold. Some guys will take significant risks to make a play, others will not attempt. Sundin was a NHL ironman for a reason. No chicken Swede jokes please, this is a respectable discussion board.
Buxton has had bad luck, and also plays the game with a somewhat reckless abandon, hence the injuries. Maybe also has lower bone density and/or a tighter wound connective tissue (ligaments, tendons, cartilage), but even if this is true, it would be a lesser contributor then the luck and reckless contribution.