Edit a page on Wikipedia:
Add a word.
Now remove that word.
Now fill in the Edit summary.
Now push Publish Changes.
Poof... not even a message like
"You pushed Publish Changes, but you didn't make any changes. Hence your Edit summary refers to no edit. Hence the whole thing has been thrown away."
Yes, if an edit is saved, one will see the message 'Your edit was saved.' momentarily.
So, no message means no save.
We have no reason to know why the user did what he did.
But it is not fair to the user to make him think it worked!
Yes, "no success message means failure." Tough luck.
Yes, because there is nothing to save... Again: Which underlying problem would such a warning solve?