I'd venture to say it's more an issue "If you're not okay with not knowing every detail, or having every detail fed to you directly, this book is not for you".
There is only one point in the narrative that some context would be helpful (or even necessary), and it's not about understanding the DCU as much as it is understanding the commentary that Morrison is making about DC politics. But not having that context, you can just ignore it as something weird that sailed over your head and not worry about it to much, if you have that kind of capacity.
The rest of it, though...the book is a challenge, in the way that Morrison's books often challenge the reader. He forces you to work, to use your own imagination, to generate your own connective tissue, to interpret as you see fit. I happen to think it's Morrison's greatest strength as a writer, something that virtually all the other greats of the industry are missing, but I can see why it's unappealing. Even I, at times, just want to read something completely light. There is a real sense of work that comes with fully reading and appreciating the dimensions of Morrison's work, but also the sense of satisfaction that comes from a good day's work.