SEGA have announced that Super Monkey Ball Banana Splitz has been delayed without confirming another release date, just saying that you'll be able to get it in the Summer of this year. They didn't confirm why the game would be delayed, but it must have been a pretty big deal for them to give up the advantage it would have had as a launch title.
There were a total of 28 third-party launch titles announced for the Vita towards the end of last year, several presumably digital titles, and 11 first-party titles including Uncharted: Golden Abyss, Reality Fighters and Everybody's Golf. With several of the games just straight ports of already released titles (like the latest Lego Harry Potter) and others new versions of major tites that have yet to be detailed in any way (like Assassin's Creed) it's safe to presume that the EU and US release won't be as populated with games as Sony would have had us believe a few months ago.
So, in short, it's likely we'll hear a few more stories like this between now and the Vita's release at the end of February.