Law or not it's the right thing to do. Being in distress With wife and family aboard I could imagin would not be a fun place. Would stop the fun for a wile on future runs as well.
Remember what comes around goes around

Nice to hear stories like this... I've always thought that you cannot have enough friends on the water.

I've heard that you should let the vessel needing assistance throw the line TO you. If you throw them the line, then you can be liable for damages. Any truth to this?

Having owned an old Pile I know how it feels to be broken down. Everytime this happened a fellow boater was always nice enough to lend a helping hand. As the times have changed I have helped out quite a few people and would do it anytime, no matter how far.

Never heard that one but I can see one reason. The family we helped was obviously no skilled in tying lines. Evidenced when they attempted to tie off to the bow rail. I'm no expert either, but I was able to tie a quick Bowline to his bow eye and it held till we got to the ramp.
By me tying the line to his boat I suppose I assumed some liability if the line snapped and injured a passenger or I tore the bow eye out of the hull or yanked a cleat off his deck. But that was the last thing on my mind.