A majority of the dragon type pokemon are dual types. So lots of them have a flying type weakness (giving them a 4X weakness to ice, partially to keep the game balanced, they have o give them at least one major weakness to be able to take them down.) It was very important in generation 1 seeing as there were no useful dragon moves, meaning you had to depend on ice to win against Lance. It's his team from the original gold and silver. However, when you rematch him, his new team is:
Also, his dragon types wouldn't be weak to electric, because dragon types are resistant to it.