Moore's Law doesn't apply to this situation because you aren't comparing CPUs designed for the same market and purpose. A low-power laptop CPU might very well be a year or more behind its desktop brethren.
Yes, it might be. It tends not to be behind several years behind though, particularly given the CPU's in a MBP.
The memory bandwidth, # of cores, fixed point and floating-point computational characteristics of MBP's are not that different from their desktop brethren (smaller, but they tend to be proportional). Bottom line is chewing half the power still puts you ahead after a couple of iterations of Moore's Law.
If your problem is bigger than that, or requires specialized hardware, it tends to make sense to support external hardware and/or distributed computation, in which case the MBP's limitations tend to matter far less.
