I believe this way people are more likely to be reasonably self-moderating and specific and less likely to engage in personally emotional argument with you than if you use e-mail. It will also give people convenience of filing a bug/suggestion without having to register on yet another bug tracker given they already have a GitHib account (who hasn't?). Needless to say using a single bug tracking system and input channel is much more convenient for everybody than if there were many.