I think that this is kinda misguided. First, Linux != Unix. Second, programming for the Linux GUI is not the same as programming for the Mac GUI. There's usually a lot of code sunk into programming an application's user interface, maybe even more than is written to implement the under-the-hood functionality. Now if Evernote had used a cross-platform toolkit for their Mac development, Qt, you might be onto something. But if they went native, then that probably doesn't translate to not "a huge job". I don't actually know what they do on the Mac, but this is a deeper question than the premise assumes.
Evernote Desktop for Windows uses the Chromium Embedded Framework. Basically, it's like Google Chrome, only with the "browser UI parts" cut out and with a different application reusing the same foundations (GUI toolkit, networking stack, etc.) So it is actually very much as if it were written in Qt. No need to rewrite anything - well, perhaps some fairly minor portions.
native linux client
in General Feature Requests
Posted
Evernote Desktop for Windows uses the Chromium Embedded Framework. Basically, it's like Google Chrome, only with the "browser UI parts" cut out and with a different application reusing the same foundations (GUI toolkit, networking stack, etc.) So it is actually very much as if it were written in Qt. No need to rewrite anything - well, perhaps some fairly minor portions.