Why do scientists think we're related to apes?

Announcing the discovery of Ardi, the 4.4 million year old fossil, they admit that they have never found any "missing link" connecting humans to apes. Yet many scientists "believe" that such a "missing link" existed, so actually apes are all our cousins, just because there's a sort of a resemblance. Isn't that like saying that obviously the sun goes around the earth, just because it sort of looks like it?