It would seem given the state of hacking and account compromises across the web right now allowing affiliates to use special characters in their passwords would allow for an added layer of security rather than using just numbers and letters?
Most non-adult companies actually prefer that you do this when signing up to publisher programs and also email you on a regular basis asking that you confirm or update your account passwords.
2-Factor Authentication would be useful to have also in some instances, especially given we're prone (generally) to allowing domain names to expire that could potentially be one for the email address used to signup at some programs
