All games require strategy to beat. Button mashing is a strategy. Not a complex one of course, but a strategy.
RTS games do require an understanding of the game mechanic and planning around it, if that's what you mean. You have to use your resources wisely, create the proper kinds of troops in order to defeat a particular enemy, and make sure your defenses are capable.
But, in my experience, they don't require a Chess level of strategy and planning, but then, I think that has more to do with the over complexity of RTS games. Chess is fairly simple, the focus is more on complex strategy given a limited set of options. RTS games are based more on how to use a complex set of options to win.
RTS games might be more strategy based if they toned down some of the gimmicky stuff involved, but then, they wouldn't look so pretty or seem so deep.
