Great question!
Most of the sugar in fruit is either glucose or fructose. Glucose replenishes muscle glycogen whereas fructose preferentially replenishes LIVER glycogen. Once liver glycogen is topped-off any extra fructose is converted to fat. High fructose consumption deranges liver function and causes insulin resistance.
So when we eat a post workout meal we would like most the carbs to be in a form that replenishes muscle glycogen. This is one of those paradoxes of nutrition. High glycemic index fruits, like grapes, have less fructose…and are likely a better option for consistent consumption. Here a re a few interesting links on the topic.
http://www.askdrsears.com/html/4/T042600.asp
http://allergyadvisor.com/Educational/sept2002_2.htm