Just like with any high purchase I either buy insurance or protection for it to make sure my device is protected. I have an iPHone 5s and I purchased the warrenty because I know if something happens to that screen accidently I'd have to fork over 269$, for an iPad Air that's 299$. A small 99$ investment in this is a great care of peace of mind
As for your 700 dollars within the two months of getting the crack, I'm not BLAMING you here but you can't be 100% sure it was the exact same matter as the previous models as that would require a vacumn and controlled enviornment that has zero outside influence. It could have been the way you walked a morning, a small drop of impact. If you have a single hairline crack often times going to your apple retail store pleading your case respectfully and if they don't talking to Apple Care tech support may get you a middle ground
You have to understand the company is there to make money, and Apple putting out a sub standard device universally which I would personally would say would be like ninty percent of the devices produces would be a call to arms, however in this case the iPad Air is selling great and while this thread is active do understand that for every problem that exists, thousands of users are happily using the device. This forum attracts the people with problems because that's what it is here for, to resolve problems
Apple isn't leaving or betraying you, it's the simple matter of production, I got two xboxes that had the red ring of death, one as a replacement. I talked to support and got it replaced twice even though one was passed the warrenty, I was respectful and got results, it helps