the thing is that might show damage (scratches, and to a lesser extent, dust) a lot easier.
Liquid metal won't scratch, as it's significantly harder than anything likely to rub against it. It will still dent however.
i think the dark charcoal colour has to do with the new UI changes in Lion rather than a material change in the apple product line.
As much as I hate to say it, as a dark grey MBP would make me very happy, I have to agree. I don't think Liquid Metal is even black to start with (what metal is?), would likely be too expensive for an entire notebook case, and a whole lot of other little reasons.