Also, there has been a number of cases when really unpopular games get featured there for many weeks, which indicates that those spots are open to paid bids from game devs to get more views, like the featured content systems like the ones in facebook and twitter, which would make sense since gives the devs a possibility to advertise their games against the odds.
Regarding the Nutaku vs DMM competition, I really don't think it can be considered that way. Try joining DMM as a fresh player and you'll see that it isn't exactly foreign friendly. You basically need to go blind in the japanese version, use Google translate and hope for the best. From a marketing perspective, it is clear that the foreign players aren't an interesting option for DMM, and it is understandable as they have the more stable, and larger japanese local market.
Finally, I would not rely so heavily on the current concept of this being an one-sided things from DMM, as we, as far as I know, only have such info from Nutaku, which isn't exactly the best reference, given previous handlings of games closures. I believe more info is needed, hopefully adding DMM's side.
From a personal point of view, given the precedents of the game still having a large player base, still having P2P paying interesting amounts of cash, etc, this incident sounds more like (another) mishandling from Nutaku of DMM titles.