The numbers from search include the people who simply weren't looking for what's on your site, no matter how brilliant the site is. G### has been trying hard (see approximately 18,000 recent threads) but so far they can't truly read the searcher's mind.
The internal numbers will always be higher because they've filtered out the people who didn't want to be there. You could even argue that the bigger the differential, the better. Three seconds to decide whether they're on the right site; three hours to settle in and read every word.