Apple builds bulletproof, toughly built stuff when they need to - for example the "pulling out the prongs" example in the discussion root article, or devices like the original "toilet seat" iBook models.
Apple doesn't do it for everything for mainly aesthetic and packaging reasons - iOS 30 pin cables are much smaller than they used to be before the iPhone came out, to fit in even smaller packaging.
I'm sure there would be complaints about the "big, ugly cable" if Apple beefed up their cables ends, especially if the only benefit would be to the 20-30% of the population that is hard on their gear, and even in that case the enhanced durability would only increase the cable's lifespan slightly.
A $5 set of Sony earphones goes through several orders of magnitude more shearing, twisting and pulling and last years. Why can't apple do that?
Because it looks pretty before it has sound engineering.