In recent years, the game has grown and entered in an era in which speed, skill and youth are the most sought after assets.
10 years ago people were trying to emulate the Ducks. Boston and LA followed suit.
Historically, the game has always emphasized size and toughness for the ideal traits of a hockey player. I feel the reason such players weren't drafted as high is because they simply weren't suited for that era of hockey.
Hughes is still very young and could grow 1-2 inches to reach 5'11 - 6'0
Erik Karlsson was listed as 5'11 in his draft year and reached 6'0
2008 NHL Draft: Erik Karlsson
I feel that the NHL is heading in a direction emphasizing speed and skill leading to smaller players entering the league. Furthermore, Hughes's game doesn't rely on his physical stature (as it shouldn't he is a small guy), I don't know if him growing will make any actual difference for his game. However, this is definitely a risky selection. The canucksarmy article regarding Hughes is a great one and erased some of my concerns about his projections as a NHLer. I love these swing for the fences picks and that we should be going for them all the time.
My theory is that the emphasis of speed vs grit will swing back and forth as the NHL is a copycat league. This means that teams will overrate and overvalue speed or grit/size as a trait leading them to mistakenly take worse players on their rosters. This will then allow teams to create better teams with players left over leading to the prominence of a new "ideal" trait. Teams will then try to emulate this dominant team. Rinse and repeat.