If that's the case, do you know why the B747 which transports the Space Shuttle does not have a split Vstab?
As mentioned earlier it effectively does, but time "buries" our perception of things. Remember that the 747 was designed first as a military heavylift plane then matured into a passenger jetliner in the 60s. The space shuttle was designed in the 70s-80s. The 225 on the other hand was purposly built with the intent of tranporting the Buran.
Also, I'm guessing that the size of the rudder is more manageable (design/structure wise at least) if it is split, that would be a pretty tall rudder if it was a single centerline unit.