The fact that just about all series have a discernable beginning, middle, and end.
In most western series, the creators will keep milking the show until it utterly jumps the shark. In Japan, a show is usually planned out from beginning to end. This allows for more dramatic and unpredictable storytelling as opposed to the whole "lets just keep things going until it gets unpopular, than change it" vibe of most western productions.
Except for Inuyasha and DBZ. >.>
But yeah I like how many animes kill shows when they need to die. Some do it too soon though.