I was used to doing it that way before changing from IDE 0022 to IDE 1.03
As of Arduino 1.0.1, it is possible to enable the internal pullup resistors with the mode INPUT_PULLUP.
Additionally, the INPUT mode explicitly disables the internal pullups.
I think that the digitalWrite to HIGH enables those pullups.
With pullup enabled the pin will read LOW on a button press to ground, opposite to 5V to button to INPUT pin.