You can complete a game without say, Security or Alteration to pick locks, but it's going to be overly difficult and require missing out on a lot.
You bring up an interesting point.
For future reference, the model should be any task can be completed via different methods/playstyles:
Opening a lock:
Thieve - pick lock skill
Mage - Open lock spell
Warrior - smash trhe darn thing open with brute force.
