im just going to put this out there.
hellsing isnt as popular as say code geass becuase of one thing, and its a very VERY simple reason, the anime hellsing was more or less shit, with a filler end, compared to code geass. the oav, havent seen any of it yet but it seams to follow the manga, VERY close.
now for part 2, OAV are NEVER as popular as an anime, they take weeks if not months to come out which leaves every LOL ANIME fag out of the loop, and only the people who generaly like the material left.
that and general dumbassery, if that is a word happens with hellsing.
now look at something like lets say beserk, which has a rather realiable when it comes out time.
or an anime what comes out every week and is on a rather tight scedual (sp)
people also prefer quanity and knowing when over quality and who the fuck knows.
list so all you know im not saying hellsing (oav or manga) is bad at all. it will be popular 1 year after it is all out, trust me on that.