Colin Clarke, community manager for BF2, writes:

Hi Guys,
  Please review the no vehicle option details below.  Hopefully this helps people understand and enjoy this feature a bit more.

No vehicles - We removed vehicles to change up the manner in which the game it played.  This places more focus on how players strategize their movements and also reinforces player skill (i.e. accuracy, etc).

Damage decrease - Prolonged gunfights that allow players to make decisions under fire. 

Commander without Artillery or Vehicles

Longer spawn time - The long respawn also creates an incentive to change up the manner in which the game is played.  There is a greater consequence on death.  We also saw the need to slow the pace of the game down somewhat in order to increase the intensity.

Longer Revive Time - This helps to compensate for the long spawn time.  With 30 seconds of revive time, there is a greater chance to be revived.  This is also beneficial since there is a greater need to revive players.  The extra time also allows for medics to give some thought as to when to revive a player.  Medics can allow dangers to pass then revive a player rather than being required to rush into danger.

Reduce health pack replenish - This is a rebalance of the medic class to prevent exploits created by the reduction in damage.

RIBs & Parachutes left in game - Some maps require water transport or parachutes to work.

TOW missile left in place