Yes.

apt-get:

  $ ls -l /etc/apt/trusted.gpg.d/

Source Installation:

  $ wget http://nmap.org/dist/sigs/nmap-6.01.tgz.asc
  $ wget http://nmap.org/dist/nmap-6.01.tgz
  $ gpg nmap-6.01.tgz.asc

This is an important part of why Debian and its derivatives are superior to OS X for web development. If you like Mac hardware like I do, at least run a Linux distro as a virtual machine and save yourself the trouble of Homebrew or its contemporaries.

The point is that most people don't do this.

Its built into apt. Unless you are suggesting that most people do:

  # apt-get --allow-unauthenticated ...

debs are authenticated.

With a .tar.gz you can verify a checksum.