Don't think phpBB allows all users to vote, I'll check a standalone board, but I looked at the coding and in the column of vote there is nothing like "AUTH_ALL"
Code:
// View Read Post News Reply Edit Delete Sticky Announce Vote Poll
$simple_auth_ary = array(
0 => array(AUTH_ALL, AUTH_ALL, AUTH_ALL, AUTH_MOD, AUTH_ALL, AUTH_REG, AUTH_REG, AUTH_MOD, AUTH_MOD, AUTH_ACL, AUTH_REG),
1 => array(AUTH_ALL, AUTH_ALL, AUTH_REG, AUTH_MOD, AUTH_REG, AUTH_REG, AUTH_REG, AUTH_MOD, AUTH_MOD, AUTH_REG, AUTH_REG),
2 => array(AUTH_REG, AUTH_REG, AUTH_REG, AUTH_MOD, AUTH_REG, AUTH_REG, AUTH_REG, AUTH_MOD, AUTH_MOD, AUTH_REG, AUTH_REG),
3 => array(AUTH_ALL, AUTH_ACL, AUTH_ACL, AUTH_ACL, AUTH_ACL, AUTH_ACL, AUTH_ACL, AUTH_ACL, AUTH_MOD, AUTH_ACL, AUTH_ACL),
4 => array(AUTH_ACL, AUTH_ACL, AUTH_ACL, AUTH_ACL, AUTH_ACL, AUTH_ACL, AUTH_ACL, AUTH_ACL, AUTH_MOD, AUTH_ACL, AUTH_ACL),
5 => array(AUTH_ALL, AUTH_MOD, AUTH_MOD, AUTH_MOD, AUTH_MOD, AUTH_MOD, AUTH_MOD, AUTH_MOD, AUTH_MOD, AUTH_MOD, AUTH_MOD),
6 => array(AUTH_MOD, AUTH_MOD, AUTH_MOD, AUTH_MOD, AUTH_MOD, AUTH_MOD, AUTH_MOD, AUTH_MOD, AUTH_MOD, AUTH_MOD, AUTH_MOD),
);
I think it will rest on reg, mod, admin, or private but not all