I suspect the reason why RU appears to have clear favourites in each competition, who then go on to win, or at least compete against each other for the prize (e.g. Sarries/Leinster in the Euro Cup) is a result of the nature of the game.
Whereas some sports, like football or hockey, allow a weak team to overcome a superior opponent because of the performance of a great goalkeeper, in RU, the team that has most of the ball, and most of the territory almost inevitably racks up the most points, thus the number of upsets is reduced.
Absolutely the nature of the game has a big part to play. The main aspect to me here is luck. While there is a lot of subjectivity in referee decisions and odd bounces if the ball in rugby, there is more of an inherent random aspect in many other sports.
This random aspect comes about because of the relative number of significant moments in a game that one team or the other can win. There is a lot more in rugby compared to most other sports.
The best comparison to illustrate the point is football vs rugby. In football, going from one end to the other isn't that big of a deal, whereas in rugby it is- if you get into the opposition 22, for example, you are more likely to score. And there are more opportunities to score from a break away anywhere on the field.
In football the scoring opportunities are few and far between, and comprise of the number of possessions where the team is able to Take a realistic shot at goal. Football games typically only have a few goals In total. If a game finished 1-1 it could easily have finished 2-1 or 1-3, as examples, with just minor differences in creating and taking opportunities. There is therefore a random aspect. Another way of looking at this is if a team scored on average 1 goal per 70 minutes then some games they will score 1, some 2, due to randomness some 0 or 3 or even 4.
A team that was half as good may score on average 1 every 140 minutes. This team will still beat the other team sometimes, just out of luck. And this is why everyone loves football, because their team is always in with a chance
Now what if their were more goals scored in football? Say one team scored 10 goals on average every 70 minutes, and the team that was half as good scored 10 goals every 140 minutes. How often would the latter beat the former? Not very. Is that intuitive?
Rugby is more like the football with more goals scored, except it's not just about goals, it's about the number of winning moments - these are the number of opportunities for the better team to dominate, hence get closer to scoring points. If your team has a better scrum and line out then every time there is a set piece there is an opportunity to get an advantage, for example.
I doubt I explained that well. Chocolate fish to anyone who got what I was saying
