The reason why stall is more consistently successful is based on my favorite analogy. If you watch college basketball, Roy Williams is the head basketball coach of the University of North Carolina, and he models his entire coaching strategy on what he dubs, "The Tiger Woods" approach. The strategy is to create as many possessions as possible because over time, the skill difference becomes more apparent with more opportunities. Since he always has the best talent, he believes that creating more possessions will give him more opportunities to win. When asked about his philosophy he says, "If you play Tiger Woods in one whole of golf, you can get a whole-in-one, or shoot the best hole of your life and beat him. But if you play him in 18 holes, you won't get lucky. He is going to bet you EVERY time." As a result, Roy Williams is the third most winningst active basketball coach today by percentage (so yeah, it works!).
Pokemon works the same way, unfortunately. When battling with an offensive team yesterday, we all know that you cannot let the opponent set up or you lose. Well, my +1 / + 1 Gyarados encounters his Gyarados, which comes in at 75% thanks to Stealth Rock. He Intimidates me obviously, but I can still kill him with Stone Edge. I Stone Edge and miss, and he Dragon Dances. It turns out we were both Adamant, max speed. From there, he wins the speed tie and OHKOs me with Stone Edge. Now, I'm facing a +1 / +1 Gyarados that my team is not equipped to handle at that point in the match. Through no fault of my own, or no skill on his part, he ended up sweeping my team and winning the match. Instances like this happen quite commonly with offensive teams, hence why many would disagree with the notion that stall teams are hurt more by hax. Bullshit. Offensive teams despise hax, because less "possessions" equals more opportunity for a game-breaking hax to ruin the game.
So in conclusion, my theory going back to this principle is that stall creates consistency because a more skilled player using stall will always beat a player with a considerably less amount of skill, therefore common stall users like IPL can overcome hax at the top of the ladder so regularly. In offensive teams, you really can lose to a player you have no business losing to by shear luck.