"On the other hand, applications like airline reservations and buying concert tickets will probably always need structured data, since they rely upon the ability to accurately manage shared access to a single data item instance (i.e. the airplane or concert hall seat) so that it is sold only once and on a first come first served basis."
"Applications like purchase order approval, medical records distribution, expense report filing, engineering and repair drawing distribution, safety inspections, and so on, really do not derive any benefit from the significant effort required to structure their data."
The information in the latter list of apps is primarily consumed by end users. Even if these apps have some structure, it is primarily to aid local manipulation (such as totaling, sorting) and not something that requires a full-fledged DB.
And though no one does it today, I believe wiki's can, in-theory, become front ends for apps such as these; much like tcl can be used as scripting front end for the apps.