Re: Really, grab my wrist!
I think we are starting to over-inflate the concept of the wrist grab.
1. Neither cosa dori nor katate dori (how we do it) are great against a knife. You need to use the pinkie and ring fingers to compress and lock the wrist joint to prevent nage from rotating the wrist; not many people grab that way. Then you need to apply a (rotational) pressure that runs to uke's center and locks out the elbow and shoulder to prevent either joint from rotating. Most of us just grab the hand and let it dangle in front of our...er... center?
2. Wrist grabs are more about controlling balance and center than they are about controlling the arm. Lock up the arm (like a chain rotated to compress the links) and that becomes a handle to control center and balance. Let a good judo player, wrestler, karate person grab you and "breaking" their grip ain't so easy. Don't even get me started on a good aikido person or DRA person. Some of the good aikido people can grab you and prevent you from doing anything. Just when you thought your tenkan was good...
I would not advocate escaping a good grab is easy. Katate dori and cosa dori are good dojo attacks and when done properly require nage to correctly move to escape. I think we have become far too comfortable with an uke that grabs your wrist and expects to be thrown. The purpose of ukewaza (in aikido) is to create a structure that requires nage to correctly move; if uke sets up a proeper structure and nage correctly moves against that structure, uke can resolve the the movement/technique. If you start ukewaza with a poor attack uke sets up a poor structure for nage.