Here's my unsolicited $0.02
I think our tanks are more like gardens than they are forests, ie., they are cultivated garden reefs, not wild reefs. Thus, it's not unreasonable to expect to have to prune and manage over the long term to maintain a balance. Like plants, some corals will grow faster and some will grow slower. Think about how a forest grows, there are distinct stages or phases. First, the quick growers fill in and compete for space, but tend to be weaker or shorter lived, followed by slower growing but longer living species. (Like here in Alberta at least, Poplars are usually among the first trees to grow after an area is forested, they live for about 30 years or so, they get ridiculously tall in that timeframe, too big for their own trunks to support their own weight, so they start dieing off or falling in windstorms, leaving openings for slower growing, but longer living or stronger tree species to fill in. And so on...)
So I would think that in the wild reefs, storms and waves do likely create some damage among species like staghorns, which break off quickly. I suspect that you don't see as much damage as you expect because there is a greater diversity of species. But I have seen reefs where the ocean floor was literally littered with staghorn rubble, which in turn is brilliant fish habitat.
But because our reef tanks tend to be collections of things that interest us, it tends to be a more random assortment of species that may not necessarily inhabit reefs in the same zones or phases in the wild.
Plus there's just the challenges of maintaining ideal flow conditions, which gets harder as pieces grow, plus the challenges of static light locations, and the fact that the bases always get shaded .... I am truly amazed when someone can grow large pieces of coral without this sort of thing happening..
This thread over at RC has some amazing large specimens:
http://reefcentral.com/forums/showth...readid=1561866
Look at this beast in particular:
How on earth someone manages to grow a piece like that in a tank, is simply beyond me. That's incredible.