Bank of America and Verizon tried the exact same practice, and customer backlash was unbelievable and the loss of business was felt financially.
If you actually start doing, I will cancel my service immediately and oh how twitter/facebook will hear about this, generating outrage and continued loss of business for Comcast.
Want to give it a go? Try me. I will not put up with this.
Edit: By the way, why was I told on the phne by a CSR there IS a $5 fee to pay online. Yet when I go to make a payment online, there is NO mention of a $5 fee? She told me the ONLY way not to get charged the $5 fee was to go pay in a local store in person. Is this true or not?