It's just not right to say any one athlete, is stronger/better/faster than all the others. Although I bet the Gold Medal decathalon winner is one of the best well rounded...
Anyways, I think the reason that people feel that a strong gymnast is so impressive, is because everyone can relate and believe they could have been a great gymnast. So for them, a person that is able to perform these feats of strength using their bodyweight, is more impressive than a man able to clean and jerk 500+ lbs. Not everyone can be the strongest man in the world, they just may not be born big enough. But you take a little kid and show him the ropes in gymnastics or any sport for that matter, and given enough work they may be the next world champ.
To put this opinion in a frame of reference, I was a competitive gymnast when I was young. Now I am an aspiring olympic lifter (my first meet will be in late june).
With that said, I have been training in a powerlifting gym lately, and something has dawned on me. No matter what I do, I will never lift the heaviest weight ever. Now to be honest I don't really mind, because I just love the feeling of lifting. But it is a little disappointing to realize, that I can never be the best out there. Maybe for my weight class or something (not likely haha), but I want to be the best ever. This may be a reason for the lack of popularity in weightlifting (I said weightlifting, not bodybuilding). In gymnastics, its just you and your body and how you control it. Nothing can hinder you but your mind.
Now you could say that I also would never be a NFL running back, and I would probably have to agree with you. But somewhere deep down inside I believe that I could be a good enough football player and be fast enough (yes I would do a lot of lifting to help...) to be the best damn running back they have ever seen.