I guess it comes down to how much you enjoy tearing your hair out fixing other peoples bugs or dealing with their crappy hardware.
I've used a 2010 MBA running OS X and Win 7 for the last 4 years. I max'ed out its specs back then and paid about $2k, including an Apple Care warranty which has since expired unused. I've had at least half a dozen Thinkpads before this, and none of them ever came close to surviving this long. My first Thinkpad was a 600, followed by a T20, etc. My last Thinkpad, a T410s, lasted less than 13 months before the LCD failed, same as a dozen others just like it around the office purchased around the same time. That's when I bought the MBA on my own dime.
Part of it is this MBA hit a sweet spot in the upgrade cycle where SSD/CPU/RAM has proven good enough to keep for 4 years, and really shows little signs of slowing for most workloads, and could keep going strong for several years longer.
But the physical hardware has held up astonishingly well. It's the most stable PC running Windows I've ever had. Thinking back on it... I don't think it has EVER blue screened, and I never reboot it except for critical updates.
The only gripe I have with the hardware is the Windows BootCamp driver for the combined mic/headphone jack doesn't switch the mic on when you plug in a proper headset, so it's stuck using the internal mic. But the built-in mic is so good, I've never bothered buying the $20 USB mic to workaround the issue.
It would be hard to tally the number of hours saved on NOT having to upgrade hardware, NOT having to replaced failed components, and NOT struggling with general driver instability and blue screens the last 4 years. This laptop has paid for itself many, many times over. Given the success I've had with the MBA, personally, when I do finally break down and buy another machine, it would be another MBA without a moments hesitation over Apple's 40% gross margin.
