The point is and I stress again that when these alliances were originally vaunted to the customer sometime ago now it is true the concept revolved around 'seamless service' that concept is no longer being followed at One World clearly
The so called 'contract' terms of carriage on most airline tickets are unlikely to be upheld in many nations as in many ways deemed 'unfair' or inadequate - the precidents set as such will overtake any 'binding' or upholding of that contract regardless of whatever that contract is for...in this case the term 'reasonably expect' would come into play i.e. pax flies on BA and recieved X or Y and therefore if BA sold him a ticket which turns out he flies on IB he can 'reasonably expect' the service/product he receives on BA - if however pax buys ticket direct from IB then this clearly would not apply - simple and commonplace legal directions particularly seen under UK consumer protection enforcement