At the end-user level I think Debian has a logical flaw.
It presumes that all software is always available in a repository
(be it FOSS/proprietary, trusted/untrusted, whatever distinction).
Yesterday I found a program (in beta) whose functional writeup was
interesting. In the latest revision a deb package was added to the
previously available formats. I downloaded the package with my
Windows machine (it was available at the instant). I now have a deb
package on a flash drive which Debian can read but has no built-in
convenient method to install.