There are currently many circumstances where use of the 'w' commands is not allowed. In most of these circumstances, imo disallowing it hinders the player.

While poisoned: It would be very helpful if 'w' commands were allowed, but stopped the waiting or moving as soon as the player receives any damage. This would make the usual strategy of applying first aid after each turn where you receive damage much easier. As it is currently, it takes up a lot of real life time to do so, because you need to check for the "you feel the poison coursing through your vain" message after every action.

- press 5
- look at screen, check: no poison message
- press 5
- look at screen, check: no poison message
.... x 20
- press 5
- look at screen, check: poison!
- apply first aid

real life time consumed: 2 minutes

While this could be:
- press w5
receive poison damage after 20 turns
- apply first aid

real life time consumed: 2 seconds

Not to mention that poison is often not a serious danger at all when your character is strong enough.

A second, different case is when there are non-hostile monsters standing next to the character. That forbids 'w' commands, too. This is tedious when you want to wait many turns in Terinyo or Dwarftown.