You have to remember that Linux does not only run on modern PC, or only on PC for that matter.
For example, one of Linux/Unix' strength is the ease with which you can setup "thin clients", or if you prefer: "dumb terminals". I use one such at home: see "nomade" in the signature. This laptop wouldn't cope with a modern GUI and several modern applications at once. My main PC, however, does (see "sedentaire" in signature). Hence I use "nomade" at 99% connected to "sedentaire" as a X terminal: I login on my sedentaire GUI account from the laptop, which is thus very valueable.
And guess what? This laptop is unable to run any 2.6-based distro!