In Nanoha's defense, the first 2 seasons did fairly well in 13 episodes, though A's is the better example by far. (Sure, they are the same franchise, but it's possible to watch them standalone). And they didn't require outside material at all.
In fact, I used to look at A's as how to do a 13 episode series, and it's one of the few sequels which doesn't require prior knowledge to work. (It helps of course)
Post-As.... yea. I get what you guys mean.
But please don't use Angel Beats as standard for one cour anime.
Serial experiments lain and Paranoia agent would be better measuring sticks. Or maybe even Sola.