Jimmy Walker is a relatively long hitter, but not one of the real bombers.
Just looked him up - 17th on the PGA tour in driving distance with 301 yards average.
Tiger has an average of 323 this year so far (according to here: http://www.pgatour.com/players/player.08793.tiger-woods.html/statistics not a large sample data though) though so he can throttle back and still comfortably keep up. Even if Tigers average was 300, he doesnt need to welly the driver every hole anyway.