[Mart]

Disc brakes don't have return springs. That's true. The pads rely on free play in the bearings to knock the pads back. Excessive free play can cause a problem because the pads have to move too far before clamping the disc.

I think the rubber seals may also play their part in bringing the pads off the disc a small distance, but I'm not sure.

The bit about excessive free play leading to pad knock back is right, though.