iOS needs to open up API for contextual menus. There's no reason why we must c/p data between apps like little apple monkeys!
Integration of Twitter an Facebook sharing options on a system level is an attempt of making data more portable between apps and services, but only in its most basic form. They are not even the tip of the iceberg of possibilities for improving the workflow of other applications and thus overall usefulness of the entire platform.
The current limitations seem to be of design and political nature, rather than technological. The potential sea of contextual options installed by apps could easily be controlled by the user from global settings menu in a similar fashion as location services.