Str82u - 9:50 am on May 14, 2013 (gmt 0)
Oh my no, for that I wasn't referring to naturally occurring, natural errors.
Those links happen naturally on the Internet
I'm inclined to agree with you though, the way you put it especially, 404 links are natural. Even purposeful bad linking domains vanish. I've found, since posting last, that about 25% are either expired or the host shut them down. For the really bad ones we do a bit better than 404.
On a similar note; Some links we used to have to our own sites that have been removed for 2 years or more are still listed so it's obvious that GWT is a bit behind to begin with.