local variables in Perl and Lua

I didnt get an answer for this in the Python thread, so I'll ask here: Why do variables have to have the local keyword to make their scope local? Why cant it just use implicit lexical scope like most any other languages?

>>17
How else a complete noob would implement variables for his quick and dirty "Personal Home Page" language? Of course he then realizes that error of his ways, but it will be already too late and we will get the next PHP/Perl/Ruby.