Memories do work on DW, if you care to use them! They just can't refer (technical limit) to posts on services other than the site itself, and LJ offers no way to export them. (We use public data feeds for every other thing that you can import; to get memories, we'd need to screen-scrape, and that gets you banned very quickly.)

So, you can use memories on DW, but you just can't import your memories from elsewhere.