pins set up as inputs are in a high impedance state, the 100 ohm really isnt even needed
This is the most common, and acceptable, configuration I have seen.
yea over the last few months it seems to be quite popular
Why? ... I dont know, new people do weird things, seems like a waste of hardware to assure that one doesnt have to actually know basic functions of software.
edit
actually the simplest way is to set your pin as input, digitalwrite it high, now its in high impedance state and uses an internal pullup resistor, connect button to pin, other side to ground, no resistors, and your logic isnt inverted from the physical state of the button (ie when the button is up the pin is high, when its down the pin is low)