Destroying stuff in sieges

[TinCow]

Thanks for the answer.
It's a strange twist of logic. CA was able to moddle crumling walls in the past just fine. Any reason they are doing it this way now?

I would guess part simplicity and part realism. They've already vastly simplified the siege system (and improved the BAI) in the last couple games by allowing units to scale castles anywhere without siege equipment. Maybe they had difficulty programming the AI to properly destroy a section of wall and then utilize that breach without also making its movements extremely predictable. At the same time, there may be a realism element to it, as the 'wall' is really just a motte covered with stone. The stone itself can be damaged, but mottes themselves are notoriously resistant to artillery. Japanese castles really did use that kind of construction on a regular basis.