Recently, after seeing a self-answer that the user had CWd (which the mods undid), I realized that CW is pretty pointless for most answers, just as it was for questions.
CW is applicable to very few answers. These are the answers that are being developed in true collaboration, and I see pretty much none of these anywhere. The only type of answer that really may need CW is the "recommendation list" answer, which isn't really allowed anyway.
If you want other people to improve an answer you've posted, then they can do so through suggested edits (and they get rep for it!). I don't see what the point of CW-ing a post is now that we have suggested edits and an effective way of getting them reviewed (namely, the new queues)
Looking through the recent CW answers on SO (ignoring those that are on CW questions, of course), I don't see any that need collaboration -- most are answers to rather localised questions. Some of them are crap posts that the user has CWd to avoid rep loss. Some are probably due to accidental CWing.
What I propose is this: Disable the "make CW" checkbox on all non-meta1 sites for answers as well. It's just as much a cheese knife as it was for questions, no need to have this extra feature lying around and being misused. If there really is a need, a moderator can make it CW, as always (or possibly a high number of edits, though I'm ambivalent about whether or not we need the auto-CW myself).
1. Metas of all kinds have quite a bit of collaborative editing of proposed policy posts/FAQ posts. Since suggested edits are disabled on per-site metas, CW is necessary in a wide range of cases. Also, ChrisF would probably stop posting on MSO if he learned that he would have to earn rep for it ;-)