The general premise of the brands not owning the properties may be true but it is far from unknown for companies to invest to get their brands into prime cities like London.
In recent years Hyatt bought the Great Eastern to get Andaz into London and Marriott bought the Berners to secure a London property for Edition (although this was sold on last week). Peninsula's parent company also recently invested in a building to secure a London property. Even IHG, which is the most asset light of the major brands, has a policy of owning the InterContinental in prime cities until it has a second property - hence the sell off of the Barclay and Park Lane after the openings of the IC Times Square and IC Westminster.