If you look at the formats poached by BBC One and Two, they have been tweaked to make them more accessible to an older audience. Don't Tell the Bride bombed on BBC One after it moved. It was too much of a 'Three' show to transfer over
I don't think Don't Tell The Bride is a good example to suggest when arguing BBC Three's case. It's a perfect example of the sort of programming that be at home on ITV2, E4 or Channel 5. The worthy shows are so far and few between, they can be accommodated by BBC One and Two quite comfortably.