Tsukihime and Fate are two sides the same setting. In Tsukihime the Throne has no (or at least, much less) of a connection to the World, so Servants can't be summoned; that's why the Vampire Apostles can run around willy-nilly. One of the big differences, but not the single biggest one, is that in the Fate side of things Edmond Dantes succeeded in finding the Treasure of Monte Cristo and then killed a lot of people, several of whom would have gone on to become Apostles in the Tsukihime setting.