Does the length of cables really matter?

Coaxial digital cables do have ideal lengths to minimize reflection and jitter. Those reflections are caused by the receiver impedance changing radically and causing reflections. Analog inputs do not have this sort of behavior, the impedance is constant.

I’ve never heard of a minimum requirement for power cables, but I do think having clean power, keeping your wall-warts out of your clean zone, and using shielded power cables can ensure the best performance.

Is this really true?

No.

And if so; what about analog interconnects?

They should be as short as possible. 1m is standard. Don't go longer unless you have to.

You can’t be two careful with those 1s and 0s. They get the j-j-jitters. 😛