From Ubuntu:
Package Dependencies
Programs often use some of the same files as each other. Rather than
putting these files into each package, a separate package can be
installed to provide them for all of the programs that need them. So,
to install a program which needs one of these files, the package
containing those files must also be installed. When a package depends
on another in this way, it is known as a package dependency. By
specifying dependencies, packages can be made smaller and simpler, and
duplicates of files and programs are mostly removed.
When you install a program, its dependencies must be installed at the
same time. Usually, most of the required dependencies will already be
installed, but a few extras may be needed, too. So, when you install a
package, don't be surprised if several other packages are installed
too - these are just dependencies which are needed for your chosen
package to function properly.
As per your question,
lubuntu-desktop
depends on the following:
lubuntu-artwork lubuntu-core lubuntu-desktop ...
Thus, the command sudo apt-get install lubuntu-desktop
installs them as well. It's inevitable.
EDIT: From Ubuntu:
apt-mark
apt-mark will change whether a package has been marked as being
automatically installed.
When you request that a package is installed, and as a result other
packages are installed to satisfy its dependencies, the dependencies
are marked as being automatically installed. Once these automatically
installed packages are no longer depended on by any manually installed
packages, they will be removed by e.g. apt-get or aptitude.
showauto
showauto is used to print a list of automatically installed
packages with each package on a new line. All automatically
installed packages will be listed if no package is given. If
packages are given only those which are automatically installed will be shown.
showmanual
showmanual can be used in the same way as showauto except that it
will print a list of manually installed packages instead.
It already says in the manpages, that it will also include its dependencies.