what drives the arm power consumption?

some interesting questions put up by shardul in the ARM orkut forum:

"what is 'it' that actually affects power consumed by a procesor...?the bus
traffic?internal register altrations?memory reads / cache
interaction?von-numann- / harvard- base?what is the factor that
differentiatessome processor designs (like ARM etc.) to be
power-efficientcompared to other processors (like x86) ?"

What indeed.. I'd say CPU Speed is a factor.. but that just means all the gates in the processor run at a lesser speed.. hence the per gate consumption is lower. but really.. what is the architecture factor that gives the edge for ARM?? I am keeping a close watch on this discussion..