There are a number of things Vim sets automatically if ~/.vimrc is present. Among them is 'nocompatible' which affects a number of other options. Additionally, Vim does try to detect the proper values for other settings based on the environment. For example, the proper value 'background' can often be auto-detected by Vim if invoked from an Xterm or compatible terminal emulator. The language settings will be based on your environmental variables.
Finally, you can run ":scriptnames" to see what files Vim has sourced since startup. This should include showing you where the system vimrc is located, if it exists.
