Site wipes also disadvantage job-hunting staffers who suddenly don't have a public published portfolio to point potential new employers / clients to. Though enterprising staffers may anticipate such moves and archive content as it's published to head off the inevitable.
(I've seen this issue raised on previous site shutdowns, quite probably Gawker.)
If you care, you should be saving your own stuff in some form. If I counted on people saving what I've written in findable form I'd have very little left. As it is, I have most things I care about.
For public-facing journalism, a public-facing record (Internet Archive, Archive Today, etc.) provides some third-party credibility that what you say you wrote and was published online actually was written when and as claimed.
Keeping your own personal clippings file preserves words but not provenance.
(I've seen this issue raised on previous site shutdowns, quite probably Gawker.)