I have a theory as to why people who play by the mathematics of the game are constantly talking about this. Where they are "expecting" to win and end up losing on the river.
How often do you actually see the river? Think about that, what % of hands do you actually see a river and how often do you force a fold when having a monster hand? What if most of the hands you are forcing your opponents out before the river are the hands where your good luck would have shown out on the river?
Now, the way I play I see a lot of rivers and more often then not, the odds seem to work out properly (i.e. I tend to lose when I saw a river and was behind, and I tend to win when I saw a river and was ahead). Now there are definitely bad luck hands, but there are also good luck hands. It all kinda works out, but only if you are actually seeing a lot of rivers and are not pushing people off their hands earlier.