The numbered titles have always come over with only three exceptions:
DQV SNES: Enix didn't want to pay for the higher capacity SNES carts, so they passed on localizing the game.
DQVI SNES: Same idea as V, but it also released really late in the SNES's life which made a localization basically a non-possibility.
DQX: It's an MMO that has constant costs associated with it for things like server maintenance, and it may have been seen as too risky a proposition to localize. I guess we still can't say for certain that it isn't coming, but after several years and many ports without one coming west, I think we can safely assume this one just is not happening.
Numbered titles skipping just does not really happen, which is nice. They're basically the one small guarantee the west gets for DQ titles.
