g1smd - 6:01 pm on May 22, 2012 (gmt 0) [edited by: g1smd at 6:55 pm (utc) on May 22, 2012]
Google treats 410 and 404 slightly differently. They recrawl every URL they have ever seen forever, however those last seen returning 410 status are scheduled at a lower priority than those returning 404 HTTP status code.*
*Conversation with Vanessa Fox and Pierre Far at SMX London last week.
[edited by: g1smd at 6:55 pm (utc) on May 22, 2012]