The rumor I always heard was that 411 was only around to stress-test their voice recognition backend. It really wasn't delivering ads or anything of revenue to them.
I've also heard rumors that Gmail and Adsense for Content aren't particularly profitable for Google. Of course I've also heard that the brand equity created with Gmail is very valuable and those two are extreme examples, but even based on similar rumors it's possible Google could shut down either one.
Rather than a rumor, it's just the way Google works. They are as data-driven as you can get. Think of all the AI work they're doing that one easily takes for granted: computer vision (image search, goggles, street view), nlp (translate, voice, search, etc), machine learning (search, et al), etc.