This meant that you got a lot of nice surprises when you played a game. TES games were particularly good like this. Daggerfall and Arena never failed to make me curious as to what else I was missing out on and what other "underground" organizations lurked in the world. Discovering Witches Covens, Necromancy groups, Dark Brother Hood Sanctuaries, Thieves Guild Nests and Vampire dens, were all found by me as I unravelled the world. Finding out about vampirism and lycanthropy stand out as seriously cool moments in my gaming life time. They briefly hinted at some of these things in the manuel but by the time you had discovered them you had forgotten all about it. So you started collecting and dissecting every cool in game book you could find about the subject you were looking for. I remember searching for dragons for ever. In vain, as we know now ha.
Bethesda have been pretty quiet on so much of Skyrim. A lot more so than Morrowind and Oblivion. Todd seems in interviews to try to say as little as possible and has even stated he doesn't want to spoil things. You could say this is a Marketing ploy but it actually seems counter productive at the moment. I've got a sneaky feeling that we will get a lot more surprises from Skyrim than previous games. Vampirism and Guilds i'm looking a you.
(Or maybe Bethesda will just release all the info a month before release to try and bombard the media, I hope not)