Well, Forgive me if i go with the opinions 100's of pro scouts, former players and my own experience as a db in my "career" lol.
Im not saying speed is the only thing that matters for a cb, but i believe it matters more than you would like to let on for them.
For 1, every cb that matters or has mattered in the league over the last umpteen years or so has been a 4.4 guy or better coming out of college..that's not an accident.
2nd, speed is the no. 1 problem rookies have trouble with when they make the leap from college to the nfl, & that's true across the board. So how do you figure it is the 6th most important attribute for a player who's job it is to shadow the fastest guys on the field? Technique can only do so much.
3rd, I think people look at the 40 in the wrong way. it doesn't just show top end speed. it also provides a very good look at acceleration, aka how fast that player can get to top end speed. This goes with the quickness & closing speed factor you cited above and has important ramifications for a cb when you are beat. And make no mistake about it, you will get beat from time to time in the NFL; depending on your closing speed, it can be the difference between a regular gain & a TD depending on the situation. To sum it up, these aren't things that you can coach up like technique, intelligence etc.
For Haden's sake, i hope his slow time was just a fluke due to terrible starting form, but no way should he be drafted in the top 10 if his 40 time is anywhere near what it was at the NFL combine, i don't care what his tape says.