Why are there so many references in Durarara? I have currently watched nine episodes of Durarara!! and I am surprised about how many references there are. Some are quite obvious (they even talk about Accel World or Spice and Wolf sometimes):



Some others not so obvious:



(It's the Baccano-screen.)

I can understand these, as all three are published by Dengeki Bunko, but why are there so many? Also, I don't understand why they included Yozakura Quartet, since it's a manga and no Light Novel?
ASCII Media Works is the parent company for Durarara's publisher (a brand company of Kadokawa), Dengeki Bunko amongst other things. This is why most of these references to shows are referenced by their light novels instead of manga. 

Durarara!! and Baccano! were written by the same person, Ryohgo Narita. The same studio (JC Staff) did the animation.

Suzuhito Yasuda is the illustrator on Ryohgo Narita's Durarara!! light novels and also the author of the Yozakura Quartet manga.

The Durarara!! and Kuroshitsuji manga are published by Square-Enix. JC Staff likes to include these sort of references in thier shows.