There's no abrupt cut-off with the CAT 4101's. They can be made to dim to a fraction of 1%, provided the PWM signal frequency has been set low enough. 150Hz seems to be that magic number. It's too bad only 2 output pins on the arduino can be configured to PWM with a frequency that low.
Forgive my ignorance, but aren't lower PWM frequencies easier to do? I know there is lots of code out there related to servo control running at ~60Hz - I'd think that you'd just have convert from a "built in" PWM philosophy to a manually-programmed PWM where you program discrete pulses at a given length?