I don't think that really determinates the quality of player, in fact some of the best players in the world crumbled under huge pressure same as Gyan, Terry, Baggio, Donadoni, Platini just to name few, it's completely normal reaction. Not to mention that Gyan's penalty was a decisive one, as far as I remember that wasn't the case with Grosso, though in the end no matter how silly it seems penalty's are more or less a lottery.