[delecti]

Every year has a slew of animes which wrap up in 13 or 26 episodes. A sparse few go to 52. An even sparser few fit the mold you describe, but even many of those end eventually with a planned conclusion (Bleach and Dragon Ball <Suffix>).

[monetus]

Sorry, I wasn't speaking in absolutes. I'm not a pollster or statistician, so I was relaying my anecdote. I think your comment's sibling, and one of mine, elucidate why I have that anecdote.