It must take into account gmail, calendar and other google products as well. Or people just simply leave it open, I know i usually have a google tab open in my browser, i dont necessary use it all the time, but i do have it open, idk i'm just guessing. Yahoo is a bit of a surprise
Well why do you need to spend that long on google? When you search something it pretty much comes back instantly with an answer? To spend an hour and a half searching is quite impressive!