Although I am a fujoshi and I adore Kuroshitsuji, I think the ambiguity of the homoerotic tension is what makes Kuroshitsuji so awesome. If that tension were fulfilled, I fear it would become "just another yaoi". As it is now, It's like it draws you in BECAUSE you know nothing sexual will happen. Yet, that sexual tension is still so strong. Whether between Grell and Sebastian or Ciel and Sebastian or whatever "flavor of the volume" and Sebastian (lol) it all becomes fodder for amazing fantasies, doujinshi and fanfic. Kuroshitsuji has a reach that a typical yaoi couldn't touch.
Toboso wanted Kuroshitsuji to evolve into Yaoi but the editor said NOPE. I guess this collection is a hint of that frustration for not being able to do what she wanted with her story. Weird since all the people I know who read Kuroshitsuji are fujoshi's anyway so it's not like the popularity would have gone down