If BA have decided to go for the door option on the 'suites,' then this makes complete sense, the customer has the nice choice of whether they want complete privacy or not.
Especially in todays flying with connectivity in the sky, people can close their door on the suite and get their heads down to crack on with work or sleep etc with less distractions, possibly no distractions (with a DND option). Or they can choose to have the door open and still have the same experience they are accustomed to with the 'no-door-seat' product. Thats the great thing about a door, it can opened or closed! Goes without saying really.
