For the tone control:

The tone circuit is a high-pass filter to ground. The more the pot is turned down the lower the threshold frequency that is passed to ground and not to the amp. So a higher pot value will retain more top end.

For the volume:

True, the volume control is simply a voltage divider, but one has to take into account that the pick up is an inductor (I think you could model it as an inductor in parallel with a voltage source) - so the pot value would have some effect on frequency response. How much I don't really know.