Should users be prompted to explain edits rather than merely describe them? Or, to steal the catchphrase about code comments: say why, not what.
The current text explicitly asks for description:
briefly describe your changes (corrected spelling, fixed grammar, improved formatting)
However, it is important to explain some edits. This is where the issue is a community one, and that's actually more important than the technical help text. Most users will probably end up taking the lead of others and copying the formats they see. In order to "steer" this mechanism, we need to have some awareness of the issue on Meta, but also not provide bad examples to users.
Conversely, it is noise to have generic summaries that contain no information—worse than the generated "deleted XXX characters in body; edited tags". (I've been guilty of this myself too.) I've seen users apply the exact same "summary" on every edit, such as "Minor edit: grammar/spelling/case/punctuation/etc." It's often used when several of those don't even apply, and there's no benefit.
I'd suggest posting an FAQ entry with guidelines (or just addressing it in one of the current FAQs) and changing the given text above to:
briefly explain your changes
I would not give examples, so no one is prompted to use them exactly; the previous examples aren't any good anyway. An additional link could be used to provide more information (including examples), if desired. (But I don't see the need for a link, myself.)