I hold my players to a certain standard. Tearing people new assholes isn't part of that. It's completely the prerogative of a GM to dictate what s/he wants for their RP, but being a tosser about it isn't. If someone doesn't meet the standards a GM sets out they should approach that person and attempt to constructively discuss it. Some people want to assure themselves of a certain quality of writing. Some put frequent posting ahead of quality and some demand a mix of both.

Tl;dr GMs have every right to impose standards but really should be nice about it.