For the same reason you can only mirror a display on the imac, emac, and ibook. There are many professional graphics users who don't need as much power as the G5 gives but benefit from lots of screen real estate. Examples being web design, the majority of Photoshop use, and logging/capturing in Final Cut Pro. All of these aren't taxing on processors because you're just doing simple repetitive tasks rather than serious data crunching but are much easier for the user when you can see a lot on the desktop. However, Apple's profit margins are MUCH higher when you buy a G5 desktop (instead of, say, a new headless 1024x768 imac) with no built in LCD display or a pretty, over engineered case. I love my mac to pieces but it drives me nuts when Apple tries to tell me that $1000 is a good deal for a LOW RESOLUTION (I can get and do get better from a cheap 19"crt, thank you) screen for my bloody computer and $1500 is a good price for an extremely low-end workstation with no RAM that takes up all of the room under one side of my desk