I've suggested this long ago as well.  Mods frequently send PMs to a member "assuming" that he or she will see their message.  They have no clue that the person they have sent the PM to will actually be able to see it.  So, when whatever it was in the PM isn't reacted to, they "assume" the person is a trouble maker at the least, or at best, the intended recipient misses out on some important communication.  On the opposite side, a non VIP member has no way to communicate with a moderator for questions about the boards or TER in general.  This is really a much needed feature.