CodeIgniter PHP4 or PHP5

[eluser]Unknown[/eluser]
the documentation states that CodeIgniter is php5

why is there this warning then in the documenation?

Note: You'll notice that the above get_instance() function is being passed by reference:

$CI =& get_instance();

This is very important. Assigning by reference allows you to use the original CodeIgniter object rather than creating a copy of it.

PHP5 doesnt need this - as objects should be passed as reference by default, should they not?
thx for any clarification.