And equally likely, just because you 'buy into the big-name' reputation/advertising:

Big name brand quality control: "Nobody will notice if we use the cheaper fibers here -as with all CF bikes, it clearly exceeds the failure capacity that humans can inflict on it out of a crash."

I think you're fooling yourself if you actually think your CF frame has been individually tested and QC'd before you buy it. Aside from the very top end bikes, they're shipped out as-is, and if something's wrong with it, you find out when you receive it.

Don't get me wrong - I wouldn't buy stuff from Alibaba.com (Chinese cheap products) no matter what due to the serious QC issues, and I would not have touched a CF frame from asia sold on ebay in the early years of CF bikes for the same reason. However, time and userbase have proven that they're reliable and don't fail catastrophically. To the point that companies like PedalForce are happy to make a brand around them, as well as others who want a smoother customer sevice experience.

But I wouldn't expect Giant or Trek to stand up for their CF frame any more than the big volume seller I got it on Ebay from - if anything, I'm likely to get more of a response from the ebay guy nowadays since there is a direct, public feedback system you can post on with ebay, whereas Giant and Trek can run you in circles and nobody would know for the better. The main advantage from buying a major brand bike from me is really the LBS support - if you have a good LBS, THEY will support the bike and any potential problems with it. I don't put any stock into the mother company (Trek, Giant) helping me more than trivial amounts. (If a frame failed, everyone would replace it - even the ebay guy.)