In message f30e42de0608070717x7b6726al462b582a4d3e854e@mail.gmail.com, Stephen Bain stephen.bain-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org writes
You should ask the developers why this was implemented as a magic word in the first place, I'm not really sure of their reasons.
Most likely it was a very quick and easy way to make a large number of existing ISBN numbers suddenly come to life.
Yes, I would imagine that that would be why. That's probably why so many variations will actually work and produce viable links, to account for inconsistent usage in the past.
It's been a magic word since before I discovered Wikipedia (in early 2003), which was quite a while before we had templates.