g1smd - 12:02 pm on Dec 1, 2012 (gmt 0)

Yes, as jdMorgan used to say:

"404 - the server can't find it, doesn't know why it is missing, doesn't know if it is ever coming back, and doesn't atually know if it ever existed in the first place."

"410 - it was here at some time in the past but now it has gone away forever. Don't bother asking for it again as you'll likely get the same response every time."

Once Google sees a URL starting to return 404, they check it up to twice more in the next 24 to 48 hours and then don't come back again for many weeks.

Once Google sees 410 Gone, they don't come back for many months to check the status again.

Google does check every URL they have ever seen at least once or twice per year because a large number of URLs returning 410 and other such codes do eventuallycome back to life (new content, new site owners, change of CMS, and many other reasons).