@bikeman it's an idiomatic expression. It only sounds right to us because we've been hearing it our whole lives. It doesn't really make sense, when you think about it. Cold rocks used to be used to cool whiskey instead of ice, and it probably started like "pour it on the rocks".
"on ice" is an entertainment term because it sounds nicer and is shorter. If I think of an ice hockey coach telling someone to practice, I think of "Go get on the ice!"
@anzpur@publicwan @gozu Thanks. Now I feel that "the rocks" is a figurative phrase as if whiskey is poured on an rocky iceberg although I don't know why "the" is used. Anyway, I see that's an idiom. I also understand the difference between "on ice" and "on the ice". It reminds me of "think different" (an Apple slogan) and "think differently".