I expected the Wii U to pass Vita sales within a few months as well. Unfortunately many titles got delayed or cancelled like Rayman, Aliens, W101, Wii Fit U and Pikmin 3. There also wasn't marketing at all and Nintendo claims to change that this Christmas.
If Wii U will ever pass Vita sales? Very easily. There's a very good chance it'll happen this year already. Nintendo is about the release Donkey Kong Country Tropical Freeze, WindWaker HD, Wonderful 101, Sonic Lost Worlds and most importantly...Mario 3D World BEFORE Christmas (!). Those are very strong titles and do NOT underestimate a Mario game. Look what it did with 3DS. Eventually Wii U will pick up more sales than Vita when the new Zelda, Smash Bros and Mario Kart releases. Sony doesn't really have a sales booster themselves like Nintendo. They also lost Monster Hunter and Dragon Quest and third parties aren't interested in Vita. Sony needs third party to sell consoles.