"Moderators" are not the same as "tutors". Mods help run the forums for the Admin, taking care of minor problems, etc. Tutors are people who help others. As such, anybody who feels qualifed to offer assistance to others may post replies to questions.
There have been quite a few student-posters who helped other students in lower levels. For instance, calculus students might help algebra students, and trig students might help geometry students. Anybody who knows the material and is willing to help others is quite welcome to join in.
Thank you!
Eliz.