Maybe I should clarify. I'm sure the weight of their shots was quite strong meaning loaded with spin, but their winners are just not fast enough to be enjoyable to watch...and when you are watching two players playing against each other like this, then it is boring for me. Their regular rally shots don't seem fast. Some attacking players who attack with big and fast shots include Federer, Tsonga, Berdych, Del Potro, Soderling and I'm sure theres quite a few more. I can get some video evidence if you feel it's necessary.
I don't need video evidence to know how hard those guys are hitting. With one exception (Soderling) I've seen all of the ones you mentioned playing live from a few meters away.
I can tell you Nadal (forehand mostly) and Djokovic hit just as hard as Tsonga for example when talking about groundstrokes, and perhaps on average over the course of a match they hit harder. He just hits flatter...with a more "direct" trajectory...and "let's it fly" more often...playing the low percentage shot. I do love his style...but it is what it is.
Yes...Berdych and Del Potro hit like monsters (probably Soderling as well, haven't seen him live), but again, it's mostly due to the fact they are physically bigger, and (more importantly) hit the ball flatter.
I don't need a winner to go 100 miles / hour to think it is spectacular.
Drop shots...and regular rally crosscourt shots which turn up to be winners are just as spectacular to me, because I try to look at the subtleties of the game.
A "regular" rally shot being a winner is very interesting to me due to what happened BEFORE that rally shot...the point construction, the movement and maneuvering out of position of the other guy...etc.
The only guy who's really "sneaky special" when compared to Djoko/Nadal (well...compared with anybody else really) in your list is Federer, because he doesn't SEEM to hit the ball like a Del Potro or Berdych...he doesn't SEEM to make any effort moving, and yet he's there for every ball, and you suddenly find yourself out of position and out of time when playing against him even though he didn't seem to really crack it in a "let it fly" manner.
It's weird and awe inspiring to watch him play because it is so evident you're in the presence of greatness.