You would think, but Word has some serious efficiency problems that I can't explain. For one, it is an order of magnitude slower at simply performing word counts than tools like wc or awk. Besides that, the problem does not parallelize well, due to the long-range dependency of line breaks.

Zooming in a bit, Word also does not kern fonts as well as LaTeX, so it might be missing some logic there that would trickle down into more beautiful word spacing and text flow.