5) Docker disintermediates distribution people and packaging subsystems.
Software built for Docker runs on many Linux platforms with a reduced overhead investment in any particular Linux distribution. Many engineering teams have a DEB guy or a RPM guy, which is a payroll slot that can be recovered for primary development.
Ever had an upstream package maintainer refuse to fix a bug in one of your dependencies because "reasons" or put their hand out when you ask for a distro package to be updated? Many expensively uncooperative middlemen can now be removed from your engineering lifecycle.
This is why CoreOS is a thing and why Microsoft is eagerly interested in supporting this technology. Docker has the potential to greatly reduce the value and competitive advantage that companies like Canonical and RedHat provide in the Linux ecosystem.