I don't know how much Dragon Quest X is going to change the big picture. I mean, it's not like the Wii ISN'T selling. There's already no reason for third-parties to ignore the Wii with the sales numbers it has, and yet for the most part they are. Dragon Quest X is just going to add to the Wii sales pile-on, adding tens of millions of Wiis to the system's lifetime sales. That's huge, but it's not like it's going to give third-parties that are already ignoring its massive userbase impetus to change their minds. It seems like their mind is already made up as to what will and will not sell on the platform. Maybe this will change, but I'm too cynical to believe it.
I can see the logic though, don't get me wrong. Street Fighter II was huge for the SNES, and it almost singlehandedly saved the system. However, I think this is a bit of a different case for one main reason: hardware. Now, I'm not saying that you CAN'T do all types of games on the Wii. Even though it's not as powerful as the PS3 and 360, it can do anything that the PS2/GameCube can, and both of those consoles had plenty of "hardcore" games. However, in that generation all hardware was 1:1 in terms of performance, basically. GameCube and XBox were marginally more powerful than PS2, but there was nothing like the performance gap that exists between the Wii and PS3/360. The same holds true for the SNES and Genesis; they were basically 1:1 performance-wise, so the decision regarding whether or not to develop games on either platform typically had nothing to do with hardware.
In this generation, that isn't the case. You already have third-parties not developing on Wii simply because they want to design games that take advantage of the best hardware out there and everything it can do. That means their primary focus is on PC, PS3, and 360 (especially since they can port their code across all three platforms in much less time than it would take them to create a Wii game - concept, design, engine, and all - for Wii). They couldn't give a rip about the Wii's motion controls because the console can't create the type of graphically immersive world that they want, or they can't do as robust an online mode as they want to. I'm not saying this is right, or wrong, or good or bad business. But I think it's the case. Sure, tons of third-parties make games for the DS, but the expectations on a handheld are lower than on a console from both developers and gamers. On the Wii I can easily see developers saying, "OK, here's the game we want to make. We can put it on Wii, but we'd have to rework a whole lot of stuff, make a completely new graphics engine from scratch, and basically compromise our vision to a certain degree. And on top of that, we're not even sure if the Wii audience will be receptive to it. I think it's safer to do it on PC and then port it to PS3/360."
It's not as simple a choice as in the past. It used to be that companies could just sit back and pick the sales frontrunner, because their games would look the same and be designed in the same way across all the platforms out there. This time around, the Wii seems to be seen as a "specialty" market that not every developer wants to wade into.