Without an internal pull-up enabled in our circuit, the button would be "floating" when open and ground when pushed. We want it to be a digital high when open. We need the pull-up resistor. (Micah Carrick)

Once again, modern parts require lower currents, but if a switch seems to be unreliable, try increasing the current by reducing the value of the pull-up resistor. (The errant engineer)

So determine if parts count or cost come into play with this design, are you building 3 prototypes or 10,000 units [to determine the cost and impact of the resistor]. Next determine if the resistor is really required, check the IC logic family being used, it may or may not require a pull-up resistor. (Leroy Davis)