"Duke, does your opinion change if I am only interested in good bass at a single location in the room?"
If you're going to be equalizing for that single location, I can only think of one theoretical disadvantage of using just one sub: If you have a significant dip at that location, you could conceivably overtax your sub trying to fill it in with EQ. That being said, dips are subjectively much more benign than peaks.
I have been told by someone who tried it both ways that the distributed multisub system sounded more natural in the sweet spot than a single equalized ubersub, but that could have been due to other factors. And my sample size (in this case, one) is too small to draw any conclusions from.
Duke