I'm not Barastrondo nor in his group, but speaking as someone on his side of the debate...
Now I'm curious, B. In the games you and your group play, does a player character never have a one-on-one conversation with a non-player character, like a family member or a contact or a mistress?
Sure, it happens. But we try to limit the amount of that. If I could think of a way to handle it without making everyone else at the table sit and wait, I would.
Does a player character never scout ahead?
Yes. When this happens, however, the activity currently taking place is, "The party is receiving information from the DM," and everyone listens even though their characters don't yet know what's happening. It's pretty rare for the scout to do much beyond "I go, I roll some Stealth checks, I see, I come back."
And if the scout botches the Stealth check and gets jumped by something nasty, we'll act in initiative order just like normal. The scout is advised that screaming bloody murder is a free action.
Do the player characters never split up to cover more ground?
Hell no. What do you think they are, stupid? NEVER SPLIT THE PARTY!
Do one or two player characters never stand guard while the rest are sleeping?
Of course, but when something interesting happens, they wake everybody up. That's the point of posting a watch.
To address your underlying point: Yes, there are situations when some PCs, or even all the PCs but one, are not able to participate in the action. That doesn't change the fact that having non-participating players is a bad thing; it's just that sometimes it's a necessary evil. We try to limit how often it happens, and we're pretty generous about "kibbitzing" - the players of the non-active PCs can make suggestions or ask questions on behalf of the active ones.
In combat, it is seldom necessary to have stun-type effects purely for verisimilitude. A dragon's fear ability, for instance, could be modeled any number of ways. So, I would contend that a lot of the combat conditions that result in non-participating players are
unnecessary evils.