Good question!! Different people DO have different ideas regarding what the "perfect body" is, and it also changes with the times. Until recently (the past 20 or 30 years), most judges were looking not so much for huge, oversized muscles, as for symmetry and the "Greek" type of figure: smooth curves, good muscle definition, a "classical" figure.... in other words, the ideal figure for an active, athletic man who has developed his muscles very well and has all the right proportions. NOW, however, the focus seems to have shifted to just plain freakishly HUGE muscles..... forget about symmetry and proportions, just max out whatever you can...yuck!!! I think its shifting back towards the Greek ideal at last, however... take a look at some images of Greek statues and pottery paintings to see what i mean.... these guys are ATHLETES, not freaks.
The reason people win again and again is because the things judges look for, change rather slowly: they're going to be looking for pretty much the same thing this year as they did last year. Muscle building on a competative level takes a lot of time and effort, so young blood and fresh faces don't pop up out of nowhere: they take a good while to develop. So, the entire scene tends to change slowly... people rise to the top, stay there for up to a decade, then fade away as Young Blood comes up through the ranks to challenge them.