This is the much like the rule the NFL has regarding stadium replays. Most plays are replayed on the big screen but anything borderline controversial is not allowed. But I think this is a minor issue, showing he replay in stadium has nothing to do with implementing technology for certain situations in major competitions. If it were limited to the goal line in the WC, Euro Cup, etc, it would be helpful in settling unjust situations. I think the offside's plays would be much harder to include.
