Having to support search engines myself in the past, I can tell you this is extremely difficult to get 100% right, especially whem there is explosive growth. In the end, I joined the crowd that leaves this with the folks that make money with it and have the structure to expand infrastructure and improve search algorithms continuously. It doesn't mean the internal search is useless, as it can search for certain parts of the forum (users, etc.) not crawled by google, but for regular posts it is harder to keep up.