[DTV]

Those programmes are all made specifically for the BBC One domestic audience.  I always thought the simulcasting on the NC was as a finance saving and schedule filler more than anything else.

I think that simulcasting has definitely become cost-saving in recent years, but when it started I'm not sure that it was the only reason. Though the changes did coincide with a round of cuts, I think these were largely met by axing Business Today and the morning BBC World News bulletin. The wider 2006 News 24 schedule changes didn't involve any cuts to presenter numbers and saw the channel opting out of Breakfast at 08:30 rather than 09:00. Officially the changes were more about things like 'a greater integration of BBC News', etc.

One factor that definitely was key, though, was the duplication of resources by having two similar programmes on at once. When in standard 'extended bulletin' mode, News 24 at 13:00, 18:00 and 22:00 would often act like a tape delay for BBC One anyway. Arguably it would have made more sense to instead simulcast with BBC World at these points as it would be far less likely to cover the same stories (these were the days when only internationally important UK news found its way onto BBC World). But network bulletins were chosen instead.

Also worth remembering, IIRC, in the early days of the network simulcasts News 24 were fairly relaxed about dropping the simulcasts (particularly One and Six) if there was breaking news on.