I think we have a fundamentally different understanding of the purpose of these exercises. I'm looking at this as having a purpose of taking people who aren't terribly comfortable with the process of creative writing and guiding them through what they really need to know for a given subject. You seem to be looking at it as just providing prompts and the user will figure it all out on their own. I feel confident saying that your method will likely not produce the results you're hoping to help people achieve. That is, actually becoming better game writers.
"Show, don't tell" is the number one lesson I would impart to new writers. Most experienced authors already take this lesson to heart, but sometimes a well-placed reminder can be helpful.
Although I'm more experienced w/r/t this style when applied to poetry writing, it may be applicable to PBP gaming. More info here: http://en.wikipedia.org/wiki/Show,_don't_tell