The thing is, in a perfect world the order makes sense. The worse graphics, less definitive version first as a bit of a taster, and to ensure hardcore (well, moderately hardcore) fans will still get the handheld version even though they've got the home console.
But in reality, with context, we all know the Wii U needed this and the 3DS didn't, so this is a very questionable decision. Lots of potential buyers now in the position of already having a version of the game and not needing the Wii U to play it.
I can think of some reasons for this. Maybe the Wii U version needs more time, but they don't want to be seen delaying Smash Bros, so want to tide people over with the 3DS one. Maybe other Wii U games aren't ready, so they can't release Smash any earlier without having nothing for the holidays.
I just hope that this doesn't hurt the Wii U as much as people are thinking. Maybe they can find a way to use 3DS smash to convince people to get it for a Wii U... doubtful, I know, but we can hope.
One thing I wouldn't be worried about is the 3DS being the definitive version, or getting more content with its unique game mode. I think it is clear the Wii U version will be the definitive version, and I imagine the announcement of the 3DS exclusive game mode is less about the 3DS having more than it is about the Wii U having something better that they haven't revealed yet. Of course, that won't matter for sales, as we all know having quality in games isn't enough, but for those that want to get the Wii U anyway need not worry about it getting neglected in terms of quality (I think).
Essay Pro