Let's first look at what Community Wiki posts do:
- Greatly lower the reputation requirement for editing the post
- Prevent the post from yielding reputation from votes
- Reduce the profile of the attribution
Edit reputation requirement
A big issue with the reputation requirement on meta (the exception being MSE), where these faq posts are hosted, is that there are no suggested edits. An edit can only be done by higher-reputation users.
faq posts are generally about one subject at a time, with one all-encompassing answer to that subject. This means that, whenever something changes about the state of affairs regarding that faq post, it should be easy to amend and update, rather than requiring someone with high-reputation to edit it. There is, essentially, no way (except for a flag) to inform these high-reputation users of the necessary edit.
That said, by the nature of the SE system, such a post would become a Community Wiki organically - after a given amount of edits it is automatically converted.
Post reputation yield
That's a tricky one. See, non-MSE metas don't actually have reputation, so this seems irrelevant, doesn't it? Well, kinda. The reputation (or, rather, the computed votes) still exist, contribute to tag score and various badges.
The fundamental problem of actual reputation yield, however, is relevant only to MSE, so this can - largely - be ignored for non-MSE metas.
There's a big difference between how a Community Wiki post is attributed and how a regular post is attributed. A Community Wiki post is much more subtle, and points out rather clearly that the post is a community effort, rather than the work of a single user. faq posts are not supposed to be the work of one user, but a community aid, decision or other important notice. Attributing these (with the coverage they get) to a single user seems rather dishonest to the community at large.
In my opinion, especially that third point is a good reason to keep the Community Wiki status on faq posts, even on non-MSO metas. More often than not these faq posts aren't even original content, but instead stripped straight from MSO, so it makes sense to go with low-profile attribution.
At the end of the day, it's up to the individual site to decide, but I feel there are very good reasons to maintain this.