[Oops, I thought the OP was asking why it was required. Feel free to ignore this.]

It was done for backwards compatibility reasons.

Let's say you wrote the following program for Perl 5.8 (which didn't have a say operator):

...

sub say { log('info', @_); }

say("boo");

...
[download]

Your program should continue to work if you upgrade to Perl 5.10. Yet upgrading to 5.10 would have broken your program if say didn't require use feature qw( say ); (the relevant part of use 5.010;).