I couldn't have put it better, Tao -- thank you.Trying to make a rule such as "lose 10%" just feels like English Grammar - something English teachers like to diagram but essentially must be learned holistically.
I flunked seventh grade English because our teacher spent about 75% of the year on diagramming sentences, and I simply refused to do it. And I could write better sentences than just about anyone in the class, and damn well knew it. Later, I found out that sentence-diagramming frequently fails, and that it's easily possible to write a sentence that diagrams perfectly but makes no sense. (Hint: the diagramming process attempts to apply rules -- probably from Latin -- that aren't always valid.)
A rule -- to knock out ten percent? Doesn't work for me, nor would it work for other people who revise as they go. My current project is very spare of modifiers already, to the point that I'm tempted to add some (but I haven't -- yet).
I have edited previous works by knocking out huge chunks of boring info-dump, (not to go into what I've had to do with flash stories to drop the word count) but that's not the same as doing a first draft and then trying to choose every tenth word to delete.
Weak modifiers? What if one of your principle characters likes to sprinkle his/her/its speech with them? You risk flattening the character to streamline the text.
It just isn't that simple -- or that easy, at least for me. It might work for someone else, though, maybe even you. Embrace revision, certainly, but do it in a way that improves the story, regardless of how that affects the word count.