In reading Pub Rants, Agent Kristin Nelson had this to say about how she edits her client's work:

Sometimes it needs a bit more work (in plot or character—never in voice or in the quality of the writing)...

I've been contemplating this for a while, and here's my conclusion:

1. A writer must write a story that focuses on a combination plot and character.
2. If plot/character needs to be fixed, that can be fixed with critique groups, editing, etc.
   
3. A high quality of writing is necessary to be published.
4. Writing quality can be fixed by a good class.
   
5. A writer's viability comes from voice.
6. Voice cannot be taught.