Yes, of course this is something that Stack Overflow promotes. Editing a post to improve its content, spelling, and grammar are all legitimate uses of the edit system. In fact, to most people, the idea of "editing" would connote precisely those edits that improve grammar and style, like an editor of a newspaper or magazine article.
I honestly have no idea why you bristle at this. Improving the quality of each individual question improves the quality of the site as a whole. You are not penalized for having one of your questions edited. There's nothing wrong with making a mistake; we all do it. If someone else catches it and fixes it, then it makes sense to thank them for that, rather than complain about it or ask for a "conformity code". The conformity code includes both general standards of decency and a reasonable style guide for the English language. You could argue that editing code samples or changing the meaning of a question is "out of bounds" when it comes to edits (although there are cases where I think this is acceptable), but certainly repairing grammatical or stylistic mistakes is not one of those borderline cases.
If you really disagree with the edit that much, you are always free to roll it back.
But it's worth pointing out that this is specifically discussed in the FAQ (pay special attention to the last paragraph):
Other people can edit my posts?!
All contributions are licensed under Creative Commons and this site is collaboratively edited, like Wikipedia. If you see something that needs improvement, click edit and help us make it so!
All edits are tracked in a public revision history. To view revisions, click the edit date on the post.
If you are not comfortable with the idea of your contributions being collaboratively edited by other trusted users, this may not be the site for you.
And, in fact, related to this specific case, the site now automatically strips out multiple, superfluous punctuation marks from question titles containing them. They merely add noise, rather than imparting any actual meaning. I see very little reason why such a standard would be applied to question titles, without also logically applying to the body of a question. In this case, a real human being performed the edit, and did so carefully to ensure that there was no meaning or code inadvertently changed. Seems more than legit to me.