Nevertheless, it sounds like there is no particular advantage to any one system other than personal familiarity - particularly if one is using "non GUI" workspace. By which I presume you mean a terminal.
No. Some GUIs don't work, or don't work well. Or they take a lot of work to maintain and configure, which is time wasted from getting work done. It may be personal preference too. But the terminal emulation is typically not the driving factor.
For me, the vast majority of actual "development" work is done at a command line, with an editor (I like emacs, but don't disparage vi), using command-line tools, such as diff, git, make, and debuggers. Some of my colleagues prefer graphical editors (which range from the Xwindows version of emacs to editors they have written themselves). I know lots of people use IDEs such as eclipse, which require a GUI too.
But much (or maybe most) of the work of a developer is not actually looking at code and typing it. A lot of it is reading and writing e-mails, chatting via IM with colleagues that are spread all over the globe, reading and editing documents (design documents, requirements documents, end-user manuals, ...) which are typically written in Word or similar word processors, reading and updating project-internal wikis, and finding the right information for the job on the web. In addition, many development tasks are actually data- or performance driven, and require graphical analysis tools (which can be as simple as Excel making a graph, and can be complex graphical beasts). For a while, I spent more time making diagrams in Visio and Rational Rose than actually writing code. So developers are mostly just normal computer users, who spend a lot of their time complaining about the e-mail program their employer forces on them (there are no good ones, just varying shapes of brokenness), fighting with bugs in either MS Office or OpenOffice, and so on. Clearly, the shell window is the an important one (and I often have a dozen or two dozen shell windows open), but everything else matters too.
And this is where the quality of a GUI comes in. If a developer is continuously being interrupted because he can't get MS Outlook or Excel to work correctly, or because his desktop OS needs to reboot three times a day (either because the web browser leaked all available memory, or the Windows antivirus needed to be updated), he isn't going to get work done. A lot of it is factual: If you have ever tried to use OpenOffice in a MS-Office shop, you understand that there are significant differences and incompatibilities. At a previous employer, we had to all give up Windows, because the ClearCase source control system worked very badly on it (those were NOT fun days, not only did our machines crash all the time, we kept losing our source code modifications several times a day). A lot of it is just preference: Given my hands and my life experience (I've spent a lot of hours playing piano), I'm very keyboard-driven, and need keyboard shortcuts for everything to survive at full speed; I have colleagues who type very slowly, and mostly use the mouse. To each his own, but such preferences can heavily influence with hardware, which OS, and which GUI (KDE vs. Gnome vs. ...) to use. And in the end, it is also a question of taste. For example, we used to use IBM/Lenovo Thinkpad machines in our office, and some people loved the little red mini-joystick in the keyboard, and couldn't survive without it; others hated it and used only the track pad; while another group always carried a mouse along.
To Snurg's comment: The cost of a Mac is insignificant to a professional software developer. To begin with, here in Silicon Valley you can assume that the average developer costs his employer at least $200K-$300K a year (no, that is NOT the salary they get, a lot of that goes into office space, overhead, insurance, taxes+retirement); so a new MacBook Pro for $2K is peanuts. Plus, professional-grade laptops from other high-quality manufacturers aren't much cheaper than Macs, if any. A Mac is no longer a status symbol, since everyone has it, or has something just as good.
Anecdote: This message is being typed on my home MacBook Pro. I bought it used in 2009, for about half of retail price (it was a lease return, 2008 model). It it still alive, an indestructible machine. I spend very little money on my personally owned computers. I dread the day it will finally die (it is already on its 4th battery, 2nd touchpad, 2nd or 3rd optical drive, and at least 3rd hard disk, now a $80 SSD): While the nearest Apple store is only 20 minutes away, I really don't want to go in there and give them several K$.
