I guess they do, but way less, and maybe it won't be the real otaku that would read (or love) Naruto, as Jump is really mainstream manga everyone could read.
Anyway, I heard that info in a French documentary, they were interviewing someone from Jump who said the audience of Naruto was definitely younger in Japan than it was in France.

Also, "jôsei muki" do get gen stories in lots of fandom. I agree pairing oriented is certainly the most common doujinshi, but there are a lot of gen and gag doujinshi written by girls. I'd say more than by boys, but getting in a "dansei muki" doujinshi section is way too scary for me to get there and verify ^__-