SnotRocket said:
we started to question exactly what is an obstacle. We took the lose explaination that anything that BLOCKS movement, besides figures, would be an obstacle.
Props are defined in the first rulebook they appear in as
Obstacles
,
Other Props
,
Traps
etc.
See DJitD pgs16-17, WOD pgs4-5 and AoD pg7.
However, for some completely unknown reason FFG changed the format of the rulebook from RtL on, incl ToI and SoB, and no longer define props as obstacles etc.
Consequently newer props need to be FAQed before they can be defined as obstacles, Traps, etc. (See FAQ pg7, 12)
What is and what is not an obstacle is not in any way dependent on movement blocking (or even movement hindering - Fog, for example, is an obstacle that has no effect whatsoever on movement).
The specific props that relate to the playing of Crushing Block are not even all obstacles (though the writing sloppily refers to them as obstacles in the second part of the answer). See FAQ pg11.