I brought this up to Staff several months ago.  It has nothing to do with posting under an alias.

You can edit your post.  All edited posts just go into the review cycle whether or not you are moderated.  Staff gave me the same reason you did - some moderated members were abusing the system by submitting a mild post and then editing it with unallowed material (rude comments, forbidden topics, etc.) after it was approved and posted.  So I don't know why unmoderated users should be penalized by something that moderated users are doing.

I told Staff that this will just make unmoderated users create new posts instead of correcting the original post causing more clutter on the boards.  Sounds like a process problem to me.  They should check where the post is coming from whether it is an original or edited post.  Staff told me that some changes were going to be implemented "soon" to fix this.  This was back in April and nothing has changed so I wouldn't hold my breath.