...Apples Warranty does not cover cosmetic damage or damage caused by such damage. Its a clear cut, black and white situation.
It seems the broken BlueTooth board wasn't damaged by the impact though, according to the first post. The OP messed up by waiting to take it in to be repaired prior to the impact. So it's not so clear cut. They still repaired it, which isn't anything to complain about. But it's the comment that "They'd no longer perform any warranty work" on the system that caused the post to begin with IMO. I'd expect such a statement, but it's not the best for customer service.
Cosmetic damage from an impact, especially if it's a minor one, doesn't necessarily mean there's internal damage. You'd have to disassemble it and test the individual parts to determine the cause. That takes time, and translates into money for any company. They don't want to invest that kind of funds in warranty support. It does mean they have to draw a line somewhere, but if you open a system up, you can usually tell what happened (impact or not, as you'll find broken connectors and such). Not doing so is bad for customer service, and gives the impression (rightly so), that such a practice is being used as an excuse to refuse claims, thus saving the company money. It's a different story if they at least open it up, and give an explaination (specifics to that system, at that time) as to why it wasn't going to be covered.
I've seen many things with electronics, and even what appeared to be impact damage, was in fact a bad solder joint (i.e. run too fast, inadequate flux,...). Especially with the lead free solders on the market. They're not truly eutectic, and the microstructure isn't as good as it could be (especially when compared to leaded versions). It forms layers, as the component metals solidify at different temps, not singularly as a true eutectic alloy would. This is one of those situations that would need an extensive investigation to find, but won't be done. It's expensive (very time consuming), and unfortunately, more common than most people might think. It's usually only done to discover the causality of high failures on an assembly line.