is it me...

[Eliseu Gouveia]

...or lately, the 12-13 episode long series seem to have started rearing their heads?

Back in the day, no anime series worth its name was less than 26 episodes long.
Now, we have Elfen Lied, Sayonara Zetsubou Sensei...

Did the studios star ordering the writers to trim it down or what?

[Bakasama]

It could be for various reasons. Quality for a long running anime tends to have technical errors. Shorter tend not to have those problems unless it's a crappy studio. I've read from various reports that the anime industry isn't too well as a whole and this maybe just a way to cut costs.

[Inkthinker]

Cheaper to make less. And, generally speaking, at least so far as I've noticed, the quality on a 13 is a touch higher than on a 26... it probably boils down to having 13 good-looking episodes, or 26 mediocre ones.

[Armless Penguin]

SZS will have another season, so I suppose it could be argued that it's not technically a 13 episode series. I don't think that point is relevant though, because I think the whole "13 episode series < 26 episode series" thing is a myth, personally. There have been a number of quite good 13 episode series over the years.

[Nik Hasta]

FLCL was really short; 6 episodes long.

But then Tengen Toppa Gurren Lagann, from the same animation team was a nice 27 episodes long.

I think it's a story-based thing more than a specific preference.

[The Xenos]

Well, FLCL was direct to video (OVA) while Gurren Lagen was a TV show. Forget how these things are sold in America, look at how they were produced and first distributed in Japan.

[Armless Penguin]

If we're throwing out examples, LAIN is a good example of a high-quality 13-episode series.

[Inkthinker]

Paranoia Agent was another.

I personally like the 13-episode series. A little longer than an OVA series, but not as much of a commitment as a 26+. The problem (for me) with a longer series is that it's easier to miss a couple of episodes and, depending on the level of continuity, suddenly find yourself at a loss for what's going on.

[Sabrina_Fried]

A box set of a 13-episode TV show sells for the same price as a box set for a 26-episode TV show. Same profits, half the work.

Sabrina