Did you notice that all the clothing in the World State has zippers on it? Because in case you didn't, Huxley helps us out with his repeated "zip," "zip," "zip," often followed by "zip," and even occasionally, "ZIP!" This is as simple as it sounds: zippers = easy access. In this world of instant gratification, buttons would cause people to lose precious seconds of nakedness.
If that wasn't enough, you can probably say something about the sterilization of passions, the technology-infused perversion of sex, and the repetitive, rhythmic, almost musical sound of the zippers. Or not.