It was only meant to be a light hearted joke. However if you want a serious reply - Yahoo bought Delicious and then a few years later they decide they want to possibly close down Delicious thus panicking users everywhere. We are focused on our userbase and would not want to put our site, which some of our users rely on, in any danger of closing and thereby forcing users to lose their bookmarks.
To be honest, that sounds a little naive. If you were to become really big, would you not sell? Or just not to Yahoo? Things can change a lot in a few years.
