Wikipedia does not require that references be free to access. Most books, journals and physical newspapers fall into this category. So editors are perfectly entitled to reference paywalled articles. The fact that you can access some of these through Archive.today is really just a nice bonus. I am a bit concerned about the possibility that the service might just vanish someday, but I don't think that's a reason not to use it.
The problem is more that a lot of references will just disappear. It just so happened that earlier today I opened 4 or 5 references for an event that happened around 2009-2012. They all gave either a 404s or just redirected me to the homepage.
This is why I consider these types of archives important: not so much to bypass paywalls, but to ensure content is still available in a decade, or two decades.
The original URLs can go away just as easily as the archive.today mirrors of them, which is why Wikipedia (or any website of record) should contain links to both, IMHO.
