Andy_Langton - 3:17 pm on Apr 5, 2012 (gmt 0)
I've also worked on a number of larger sites, and would second deadsea that this isn't about a special relationship with Google. It's primarily about scale. Good sites with millions of pages also have a huge number of entry points - so they are being crawled from a number of different angles all at once. As long as internal link structure is reasonable, this can result in incredible amounts of crawler activity, and extensive coverage of pages.
Sites with a large userbase can also generate huge amounts of activity around new content very quickly, across all the mechanisms Google uses to find content - they have everything from new links, social mentions to toolbar activity.
But don't believe these sites are immune to the problems that smaller sites see. They're still agonising over analytics and monitoring indexing etc. etc. Typically, large amounts of the content they produce doesn't deliver any real search engine "return" because it doesn't get the engagement it needs - and no amount of users, links or social activity will get everything to rank. They're just have different scales of problems ;)