It is because your system protect itself from peoples trying to add files in critical area where they could affect other users. If the files stay in your home folder, then it affect only you (you can disable execution of apps in your home if you want to protect you even more).
Only root or other administrator account can install stuff system wide.
If you want to install something without root privileges, you can create a folder and specify it when you do ./configure. It work like that ./configure --prefix="/home/<path>/<to>/<folder>/"
Then, make install will install the files in the folder instead of /usr
If you have executables, you will have to add /home/<path>/<to>/<folder>/bin to the $PATH variable by adding this line at the end of your ~/.bashrc file
Last edited by Elv13; 10-04-2009 at 01:20 PM.