Well, I suppose that's yet another leftover directive that predates concern over congested airwaves...
Thirty-something years back I was taught that an "Ident" request need only be followed by pushing the button. I've followed that since, nad have only been asked for a verbal response a handful of times.
It really is silly... If you hear and comply, the controller will see the result before you can reply verbally. If it doesn't work, or you didn't hear, another verbal exchange will be required regardless.