Why can't we (BA) do something comparable
Not can't but won't. These days decisions are taken not by bold leaders with vision but by bean counters and they are not going to spend money on something they don't fly anymore. And more likely BAA will rent out the spaces around T5 to any airline that can afford to have their model placed there.
One of the nice things about France is that passion can often trump economics. Its not just at CDG. Look also in Hall 3 at Marseille-Marignane and there is one of Henri Fabre's Canard floatplanes hanging from the ceilng.