I didn't think having SSB on the 3DS was a good idea. Now since I own a 3DS and not a Wii U the whole concept is pretty favourable for me but that's the whole point. Why buy a Wii U for SSB when the 3DS, the system people actually own, provides the same basic experience? Nintendo thought that Mario would sell Wii U's but both NSMB and 3D World did not and both games had 3DS equivalents that were released first. It's like the Wii U is an extra luxury. "Buy the Wii U and get a fancier HD version of your favourite 3DS games!" It might as well be the Sega CD offering a great, but unessential game like Sonic CD, to those that want to spend more to enhance their experience. But the Wii U isn't going to sell worth a damn as an expensive accessory for the 3DS owner.
So why offer the 3DS game first unless you're trying to bury the Wii U? You did this twice already and it blew up in your face! At least those Mario games have unique levels. A multiplayer focused title like SSB is going to have a harder time selling both titles as essential purchases. They'll be more likely to come across as the same game. And I assume the whole rationale for this decision is to get people to double dip. Well that might work for someone that owns both systems but who is going to buy a Wii U for a "special edition"?
Frankly I think even having a 3DS version is self-sabotage but, hey, when the development was started the Wii U wasn't in such dire straits and if you spent time on development there's no point in canning the 3DS one now. But Nintendo can stagger these out to give the Wii U a period of exclusivity that might encourage system sales.
Not only do I NOT have to buy a Wii U for SSB I get my game FIRST! Sweet! Hell, there's probably going to be some owners of both consoles that will not get the Wii U version because they don't feel they can justify purchasing both and their impatience will make them get the 3DS version. Nintendo delayed the Gamecube version of Twilight Princess to give the Wii a boost. Anyone disagree with that decision in retrospect? So why is Nintendo doing effectively the exact opposite here?