As I wrote over yonder,
That lock reason is supposed to be used for questions with just a few community-wiki answers - in other words, answers that anyone with a nominal amount of rep can edit without needing approval. Stuff like this, where the answer is a collaborative effort built by many editors over the years.
That's still true. In order to edit an answer to a locked question, you need to have editing privileges; you can't suggest edits to answers of locked questions. The majority of questions locked for this reason are also community wiki, so this is why you don't see this often.
In this case, there actually is a fair bit of collaborative editing on the top questions, and given its frequent use as a duplicate target, I think there's a lot of value to be had in encouraging more edits - so I've taken the unusual action of converting the entire lot to CW.
That still doesn't allow suggested edits, mind you - but it does allow nearly anyone with some trivial experience on the site to contribute edits directly. Provided that isn't abused, it should suffice.