It really does depend on how we define usability. The configuration of the user interface is the details. As an architect one would not worry about usability. Not in the sense, of where to place icons, what colors to use and what are which things to make bold. HOWEVER, what the user would do with the system is an architectural concern. For example, having to store data in two separate locations within the system is an architectural concern. For example, having to copy and paste data between two spreadsheets as there is no way of sharing data. Usually, usability omissions are inconvenient, but it is likely that errors will creep in causing users issues.