Yeah, but for the situations in the first, second and last screenshots, you can't get there without using cheats. So you can't get get stuck there normally.
In the case of the pits in level 10, and also in level 9 in the situation of the third screenshot, it's true that you cannot proceed... but at least it's still possible to kill yourself.
Hey, in this case, suicide isn't possible!

The spikes never retract (because of the proximity of the impaled guard?), so they stay 'safe' to walk on.
Edit: Ah, I forgot, this one was already discovered by Norbert and discussed by David earlier in this thread.