Aside from what is essentially a corporate lobby/fiat what legal pretense is there for time or place shifting restrictions on a copyright?

The Constitution seems straightforward:
"To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries."

To whit we've had the RIAA/MPAA lobby try to redefine that limit to being "forever minus one day, and only in the following regions for the following timperiods..."