Your accounts are tied to your serial(s). XWIS is designed so that only you can use your serial forever. It's also tied to your XWIS control panel account. A person would need both your serial and access to your account to play online, however this probably violates their TOS. Even if you did give them, you would no longer have exclusive access to your XWIS names.
Pretty much the same deal with the EA games. The serials are tied to your email address/EA account(s) and can't be transferred.