I agree with you, but I have two points. 1) A good nage can sense when he/she should pull back on a technique or a throw in order to save the uke esp. when they can tell that the uke is not ready or maybe a little afraid. 2) Uke should know when nage is not paying attention and bail out, if necessary, in order to save themselves from injury. I know someone who decided to take that approach after he got injured by a thoughtless nage.
Good points! I've never been hurt by a training partner (knocks on wood) but there have been a few times where I was close and they definately left a lasting impression on me. I think the reason I've never been hurt is likely as you said, because there was that sense of when to back off a bit.