What if, for some reason, [[ADSL]] would be changed to
redirect to
another page, or become a disambiguation page rather than a redirect?
All those links to [[ADSL]] would then link to the wrong page.
Presumably it would be done when the page is parsed just before being
viewed, rather than when it's saved. I guess it would be done at the
same time as the existence of the article is checked in order to make
the link blue or red.