Actually, they can be modified.
I've got code that sets a value in $_REQUEST as part of the page initialization: it actually checks to see if an entry is set and if not, provides a default. This is because there is scads of code that just uses the entry in $_REQUEST without checking to see if it is even there...
(I filed a bug that PHP's default error level should include Notices turned on. They closed it as not a bug, citing the docs that say you should change it for development, but ignoring the fact that many developers never touch the php.ini file.)
I think what your programmer is doing is avoiding continually referencing $_REQUEST, perhaps under some impression that a direct variable lookup is faster than an array lookup. Or should I say, that it is faster enough to make a difference.
Wade.
Q:Is it proper to eat cheeseburgers with your fingers?
A:No, the fingers should be eaten separately.