Do they not pray a rosery to her as well? Is there an Our Father version of these beads to Jesus or God? No. Instead of asking Jesus to forgive their sins (going through a Priest in a confessional) they pray "holy Mary mother of God pray for us sinners"... Yet sin is forgiven through Christ and only Christ.
The concept of intercession.
The Catholic (and Orthodox) tradition is such that one can assume that certain people reside in heaven, and can be addressed directly in prayer - saints, and Mary for instance; and that it is helpful to invoke their aid.
There is a big difference of opinion on this subject with every Protestant church, including the Anglicans/Episcopalians.