Thanks for your reply marcopizzaiuolo . Your bit 'linked to selling other products within their business' is really interesting as, generally, there's a decent selection of hotels on Amex Travel but not everybody's on it (and you can't filter nicely), so perhaps an external supplier would be able to offer better variance in places to stay.

As an aside, it puzzles me why certain venues aren't on the Amex Travel list, as an example: The Newt in Somerset. It's a venue that hosts Amex Experiences in the UK but can't be found on Amex Travel website. When I last spoke to Concierge they mentioned they had access to a GDS system, I don't know if that'd give wider options than just Expedia.