That is an advantage. It reduces extraneous incentives to post links, which should be only about the information they provide and not about page views. At wikipedia's scale, and sensitivity to information purity, that's relevant.
See also the rel="nofollow" decision from a few years back.
It's probably good that it's possible to opt-out of being archived but what annoys me is a useful domain changing hands and the new owners deciding to wipe its history.
It's not wiped (they don't delete anything) but if robots.txt forbids indexing then access to old archives is blocked. It can be quite aggravating, but at least the information is not lost---if robots.txt or archive.org's policy changes, it can be retrieved again.
That is an advantage. It reduces extraneous incentives to post links, which should be only about the information they provide and not about page views. At wikipedia's scale, and sensitivity to information purity, that's relevant.
See also the rel="nofollow" decision from a few years back.