But on paper it appears that a cog has more power than each one of these limited cores. Plus historically the Propeller has been cheaper than most of the esoteric crazy Forth chips and implementations.
Its important for medium size runs. You make a couple things for a small vertical market, or custom, or R+D and it doesn't matter, any choice is like one hour of embedded developer salary so it doesn't matter. If you're doing huge runs of a million in China you "have to" use the cheapest thing out there, and this won't be it. I bet around 10K production runs is where part cost creeps out of salary rounding errors but isn't high enough to utterly force the use of something specifically designed to be cheap.
As far as cost goes TI and Microchip have some low power offerings where $20 for this forth chip or $12 for a propeller minus the cost of a cheap low power competitor means you can afford a larger battery in the budget. Or you could afford more "whatever" in another part of the design.