In 2008, jetBlue partnered with Irish flagship carrier Aer Lingus to allow passengers to switch between airlines on a single ticket for flights with connections in New York–JFK or Boston Logan. Unlike traditional codeshare agreements, the companies cannot sell seats on each other's flights, so customers initiate the purchase on one airline's website and then are transferred to the other site to complete the transaction.
Say for example there are two hotels side by side. One meets all the requirements of the Diamond classification, pool, valet etc etc. The other may have vastly better quality rooms, best furnishings, best of everything but does not have a pool. If that was your hotel, even though anyone can clearly see that it's better than the hotel next door, would you feel it's fair it won't meet the Two Diamond standards?