The Buran may be more capable in general terms than the Space Shuttle, but one thing that has to be taken into account when you talk space is "cost effective".
The Ariane 4 launcher, for example, was (no longer manufactured) a very fine launcher, and considered the safest in the world together with the Soyuz, but capable of putting in a GTO much heavier payloads.
As I said, it's no longer manufactured, as it has been replaced by the more powerful yet less reliable Ariane 5. Why? It is MUCH cheaper.
The Ariane 5 can carry up to 10 Tons now and has about 50% less parts than the Ariane 4, making it very cost-effective. True it has had some accidents, but the possibility of making dual launches makes it the preferred launcher in the world right now, with more than 40% of the commercial market.
From what I know, the Buran was a very fine piece of engineering, but it was very expensive as well... and having the Soyuz safely transporting people to space, it was more a political investment than a truly necessary one.
Even the space shuttle is barely cost effective in industrial terms, but its main "raison d'être" is the publicity of being an unique spaceship. You can do what the shuttle does with conventional launchers much cheaper, but it wouldn't be as spectacular.
Daniel