I think this is an attempt by 3E designers to simulate a 1E "Tomb of Horrors" style trap, like this: "Stone block starts dropping, DM counts to 5, anyone who doesn't say they're running is automatically crushed."
It's not perfect in 3E, tying it to the round cycle. But to me this seems like a mostly smart roleplaying challenge: Ceiling starts dropping. Everyone gets one cycle of actions. If fighter tries to hold up ceiling, he's crushed. If rogue tries to find secret door, he's crushed. If wizard runs he's fine.
It's not perfect. Feel free to run it S1-style or make up your own mechanical modification.
