The service isn't actually trivial. And I don't know if amichail has anything specific in mind, but improving the quality of a writing is not as simple as following stylistic guidelines.

First, battling over grammar and word choice shows that there are usually multiple interpretations and construction methods for a single utterance.

Second, grammar and word preferences change over time. While this makes a case for writing fashionably, it also means that really good writings are valued for content; good content can be expressed without strict adherence to guidelines. Rap, for example. It makes no sense to proofread rap.

In any case, there are no absolute rules for language use. This point is stronger when you have a large readership, and even stronger, when your readership has the ability to talk directly to the author, and perhaps even contribute.

The challenge is to be able to accomodate a huge number of these copy editors, who come and go as they please, shout or whisper their preferences, and somehow make the end useful and actually better.

"good content can be expressed without strict adherence to guidelines. Rap, for example."

Apparently, "good content" is one of those phrases subject to multiple interpretations.

my writing led to confusion and thus was not "good content." but ah, you know, good content. you know? :)

notice that dfranke just proofread my post.

I suspect that casual writers have an even greater need for such a service than professional ones.