(1) combing a no-fuss GUI and the ability to run most major proprietary apps with a UNIX underpinning. If you also want to combine that with multimedia work (serious photo and video editing, graphic and print design, DAW work, Linux is a no-player, you need either Windows or OS X. Yes, there's Inscape and a few other tools, but only outliers use them and you'll be missing on almost all major tools and commercial products).
(2) some not-found-elsewhere niceties in the hardware (great trackpad, fine display, sturdy all-one metallic, construction, top-notch SSDs, no-fuss sleep/wake, nice latch, great aesthetic, and such).
(3) works nicely as an ecosystem of products
(4) Finally, it's in resale value.
It's value is not and has never been in bang for the buck or big performance.
And it has lost points regarding (2) through the loss of magsafe (another handy exclusive feature), worsening of the keyboard, and drop of some handy ports.
>PS: I do have to say though that all their pro hardware seems to be very overpriced
Some of it is (e.g. Macbook Air/Mini/etc are long in the tooth, at this point you're paying just for the privilege of using OS X, which many don't care about that much). But their costlier models are not really overpriced, they're just high-end.
I often look to get a comparable machine for Windows, and when you add the same things from machines from Dell, IBM, Razer, you get at the same price range very soon. I'm not talking about some custom rig desktop with faster cpu and gpu, but about getting something comparable at all levels (their top of the line laptop machine, comparable monitor, ssd, construction, etc).
For me it's still worth it. I like OS X, do lots of programming work (some native, some remote thru SSH), lots of multimedia with Adobe apps and DAWs, hate tinkering (and even more so hardware tinkering and custom rigs), and don't mind paying a premium for something I use 10+ hours each day. I also don't work with .NET, in which case I'd use Windows.