Really? I've been very lucky with my numerous Windows machines. Are there really that many problems (a need for repair or replacement) with a MacBook Air?
I bought the first revision of the MBA back from 2008. They had a lot of issues that have since been ironed out (from what I've read). I won't buy another laptop that isn't a MacBook Air! I love mine to bits, even if I've needed some work done.
That said, they are machines, and could break or become defective. To me, it's worth the money for the peace of mind. My family has learnt that lesson through various Windows and Apple computers.