I work in a group in which nearly every developer has a MacBook Pro, and they are all used pretty much just for this. It's quite common. It's a cheap way of getting a relatively decent Unix workstation. We all use the terminal or iTerm2 for local development and work on remote Linux systems, and around half are vi or emacs users. The rest use a bit of Sublime Text or Eclipse depending upon what they are doing. The mac is useful for maybe 5% of each developer's work, otherwise a Linux box would be just as useful (I'm one of the outliers who uses Linux and BSD nearly exclusively.)

Certainly for our purposes, the new MacBook is pretty sub-par. All the lost connectivity options were used heavily. I doubt when the time comes around to refresh them they will be as compelling as they were in 2011-2012. I'll probably just get a stock Dell or HP and find it massively less frustrating. It's not like the old MacBook Pros didn't make compromises either, but now it's making so many its use is difficult to justify.

Don't forget that Finder can connect to sftp fileshares.

Would they be better off using KDE 5 to develop? Probably, but good luck getting your manager to sign-off on a linux laptop, especially when all the other devs use 3000€ devices to manage their xterm sessions.

So? If one likes the quality of the product, why not?