For me it's the software+hardware, and the killer feature is a unixy OS with great battery life and little to no fuss. Is it possible I could get similar results out of Linux on commodity hardware? I'd put it at long odds, but even so I bet I'd have to shut off features (losing convenience) and spend a lot of time tweaking it to make that happen.

It's not even just the OS. I've switched to Safari because losing 1.5-2 hours of battery life to use Chrome or Firefox isn't worth it. I'll just open Chrome when I really need it, use it for a few minutes, and close it.

There's also a "no one got fired for..." factor. OSX refuses to work with the client's projector in a meeting? Apple sucks. Arch Linux refuses to work with the client's projector? You suck.