Greetings,
When a new version of an already existing Linux distribution is released, what is typically added, removed or changed with the new version excluding the usual Graphical User Interface touch-ups, tweaks and alterations? In other words, just a "base or 'net' installation" of the OS without a GUI.

And also; I'm under the impression that the code base and overall size of the OS keep getting bigger and bigger with each new version (or 'release') as time continues to move forward, ...with newer versions of already existing distro's dwarfing the size of previous incarnations. Is this correct? ....For me, the end user, that would be the download and installion size. =)

Thanks

Sometimes there are practical matters that limit growth in that direction. Slackware, for example, has always needed to fit on one DVD.

it really depends on the operating system

take Fedora and RedHat
fedora will DRASTICALLY change the system from one version to the next
they might move from Gnome2 to gnome3
or move to pulse audio
or remove default software and use something very different

or Redhat
where the major version of a program that was in RHEL 6.0 WILL STILL BE USED in RHEL 6.11
the major versions will NEVER change in minor version upgrades
and current SECURITY updates are BACK PORTED to the older code

Each distro version is made by some committee. They set goals for the next distro. These people move in and out and goals change. They try to stick close to the mission or target audience. That mission might change as hardware and software change and even political issues. The most easy would be to apply roll up of security patches.

So, if you liked a distro 10 years ago, it might be quite different today.

There are only a few distro's that try to maintain size. Most mainstream distro's target a large group of hardware and users. How many times does a new hardware get produced? Well, users want to have that working in the next release and still keep backward products working.

If linux had worked insisted upon assembly we wouldn't have this issue.

Generally, a new version of a distro will include newer versions of included software, perhaps some new default software packages, and newer underlying libraries. Some distros try to be very bleeding edge (such as Fedora, as John_VV pointed out, and Ubuntu).

Other distros are more oriented towards stability (Slackware and Debian are both good examples of this); their included software packages and kernel version may lag behind those of the bleeding-edge distros, while still being newer than those in the previous release version.

What generally does not change is the overall look of the desktop/window manager, unless the distro's default desktop environment has changed significantly. Unlike with Windows version upgrades, Linux distros do not feel as if they have to change a bunch of cosmetic stuff (the way American automakers used to radically restyle cars almost ever year) to convince users that they have something new. Linux distro maintainers just want stuff to work better.