I'm going to guess that because Chaz's is a (later?) servo machine, with what would of been a pretty much totally different controller, they used different switches.

Sooty, are you sure there's not proximity sensors?
On the X, you have to either remove the front panel of the table, or unbolt the switch mounting panel from the cross slide, and the home sensor is at the right hand end of the panel.
On the Y, you have to move the table pretty much fully back, and if you lift the bellows, the prox sensor is at near the front right corner pointing straight up.
On the Z, you have to fully lower the head/spindle, and with the motor cover removed, the prox sensor is mounted inwards of the right dovetail, and should be visible just above the head/spindle casting.

The carousel has a single inductive sensor that pulses on each rotation of the Geneva mechanism, which has to rotate twice to move between tools. This is probably the most problematic part of the ATC, as you need some form of verification that the correct tool position is set on initial power up, and if the tool is currently in the spindle or not. Mach does have the option of persistent DROs, but I've got an absolute encoder which I'm going to add so I don't need to manually check tool numbers.