You haven t heard of a lot of anime then While 13 26 episodes is common for some series especially the majority that Cartoon Network licenses for Adult Swim many animes run up to 52 or into the hundreds of episodes Even with the anime that only run for 13 26 episodes the manga versions are usually much much longer The Big O manga is to my knowledge still running So is Inuyasha I believe In this case the length is more in reference to the fact that it s not terribly long in either version