Quick question: Will the AI controlled characters be better in the Wii U version than in the 3DS version because the technology is so different? Or will they keep the level of difficulty the same between the 2 versions?

I hope so but I doubt anyone knows. They do seem easier than they normally are in the 3ds demo version, thats for sure

I haven't really had that same experience.  Sometimes the level 9 CPU's seem harder than at other times.  Sometimes they seem harder than at least the Brawl level 9 CPU (haven't played Melee recently enough to remember).    Sometimes they're very easy (one time K.O.'d level 9 Villager twice in the two minutes and only received 3% dmg).  Sometimes they're pretty tough (got knocked off the map by level 9 Mario and he jumped after me and attacked me further so I couldn't recover).  It's hard to tell, especially because it's just the demo.

The CPU demo characters seem a bit inconsistent. Mega Man and Villager are easy to beat down. Link is a bit tougher. Mario and Pikachu dodge just about everything. A little harder than Brawl so far, but I'm not as familiar with these characters.