The nice thing is that a high-DPI trackpad can act as both a relative-input joystick (movement based on how far from center you are) and an absolute-input pointing device (movement based on absolute position in the device's input field).

Joysticks can do this, too, but their DPI is frequently nowhere even close to acceptable for this kind of work - they tend to be somewhere in the 200-400 DPI range, when your average mouse tends to be capable of input at several thousand DPI; if the touchpad resolution is good enough, then I think they're going to have a winner on their hands.