Unique word count and grammatical complexity...

[deathtrap]

Browsing around the forums and other learner sites you often come across stories, novels, texts and whatnot delineated by unique word count or character count such as Chinese Breeze, Graded Chinese Reader...etc. However, seeing as how vocabulary is not the sole factor in language ability I was wondering why there aren't more books that are sorted by grammatical complexity?

Is it because there is a certain limit on grammar complexity with the ceiling being much lower and is reached much quicker than vocabulary? Or is it simply much harder to quantify? Or is it that much longer books are generally going to be much more complex grammatically than shorter books/short stories?

Are there any book/text/short-story sites that sort their collections based on grammatical complexity?

[WestTexas]

Or is it simply much harder to quantify?

This, I would think. Anyone with a word list, a little programming experience, and some Chinese knowledge can write a program that counts unique words within a couple days. A program to measure grammatical complexity would require much more programming as well as grammatical knowledge. In addition, it would be a matter of opinion which structures are easier and more difficult.