whether to add "url" field in the bibtex entry

[hupili]

Refer to this comment.

[dingens]

I argue for inclusion. People who don't like them can still remove them, for example in biblatex:

\AtEveryBibitem{%
\ifentrytype{book,collection,incollection}{
    \clearfield{url}%
}{}
}

I'd also argue for linking to the html version instead of the plain text version, because it is way easier to use (toc has links, etc).

Also, they offer HTTPS now, so that should be changed, too :)