That's a fair criticism. Later posters were more accurate in saying that every move should improve your position. That's a general enough term that it can, in my opinion anyway, encompass the sorts of things you're talking about. Playing a sharp, tactical game against an opponent you know prefers quiet positional play, for example, or intentionally moving into complex tactics when the opponent is under time pressure or otherwise would be less comfortable in that situation than you would be. Kasparov is famous/notorious for the latter, IIRC.
In practice, you'll be able to do very, very well with just a solid understanding of opening principles. You don't need a huge background of memorized lines. Lots of chess players love to study opening lines and memorize craploads of them because it's easier to memorize than it is to understand.
This is another great example of what Miramon refers to above, actually. When playing against a "by the (opening) book) player," it can be advantageous to make a slightly sub-optimal move early in the opening simply because it takes your opponent out of book and into having to think about his moves, which is a situation where you have a stronger understanding. You've improved your position by maneuvering the game out of your opponents comfort zone and into yours.