When Ubisoft revealed that Rayman Legends was coming to the PS Vita, it also stated that the handheld version would include all of the content from the original game. However, according to reports from players who bought the PS Vita version of Rayman Legends, the game has 28 levels less than the versions available on other platforms.
UPDATE: Due to a longer development time than expected, Ubisoft wasn't able to to include these 28 levels in the PS Vita version of the game. However, Ubisoft already confirmed that the levels will be added via a free patch, at a later date.
The missing levels are the rock-hard "Invasion" levels, which are remixes of the completed courses but with the new layouts and hazards. In addition, the fact that these levels were removed decreases the number of Lums that can be collected, from 700 to 615.
However, the PS Vita version does have some exclusive content, the touch-controlled challenges, but compared to the missing levels, this version does come with less content overall. Ubisoft did say that the PS Vita would include all the content, so it might be possible that the remaining levels will be available via DLC.