Why throw local variable invokes moves constructor?

Recently, I've "played" with rvalues to understand their behavior. Most result didn't surprize me, but then I saw that if I throw a local variable, the move constructor is invoked.

Until then, I thought that the purpose of move semantics rules is to guarantee that object will move (and become invalid) only if the compiler can detect that it will not be used any more (as in temporary objects), or the user promise not to use it (as in std::move).

However, in the following code, none of this condition held, and my variable is still being moved (at least on g++ 4.7.3).

Why is that?

#include <iostream>
#include <string>
using namespace std;

int main() {
    string s="blabla";
    try {
        throw s;
    }
    catch(...) {
        cout<<"Exception!\n";
    }
    cout<<s; //prints nothing
}