Curious as to what is different between digital servos and ESCs interpretation of the ppm controls from the RX.

I ask as I have a really strange problem with my basher sabertooth, stock electronics + flysky 3 channel radio and reciever.

Turned it on a few days ago, and servo is fully dead. No centering torque, or noise.
Swapped ESC and servo channels. ESC/motor run just fine, servo still dead.

Aight it's a dead servo, except I tried 4 other servos I have lying around. The 2 digitals (d770 solar servo) fully dead, and I know at least one was working last time I ran the car it's on (6 months ago). The continuous rotation servo spun, but did not change speed with TX commands. Finally, a plastic geared horror I dug up was also fully dead.

Opened up stock servo. All looks fine inside, wires soldered, no cancer smell, no scorching...
Checked +/- voltage from ESC, 6.2V so that's all good.
Checked signal voltage with my multimeter. 0.6V, 0.4V and 0.3V for full one way, middle, full the other. Matches up to 2ms/50Hz 6V, 1.5ms, and 1ms fairly well. Don't have access to a scope right now unfortunately.

So yeah, any of you folks have any idea what could be busted? Or any insight into what is different between ESCs and servos control wise?