Think of it like a map. Pages are the towns. The roads are the links. In the past, Google was assigning value to towns based upon the roads that came into them. Roads from bigger towns are bigger roads and thus the value of the town that bigger road goes to is given more value. That's all fine and dandy, but we can learn as much (or more) from a map by studying the roads themselves, and not the towns that are on it.
How nice is that?