While there is a certain amount of convenience in having all the Bing apps listed under "B" in the app launcher screen, an argument can be made that's it more logical to have the apps listed under their descriptive name of choice ("news", "weather"). Shorter apps names also look better in the app launcher and are easier to read and also work better with voice commands.
Dropping the Bing name also simplifies the branding. The Bing name, more so with the arrival of Cortana in Windows Phone 8.1, is not that closely associated with Windows Phone. It's not that Bing isn't important from a technology point of view, but whether consumers really need to take on another brand name, outside the context of pure search, is debatable.
It's interesting to note that the descriptive name only approach is taken by Google, Apple, and others for their built-in and key downloadable apps (i.e. apps that you might think of as being part of the platform bundle).
The other obvious app group branding on Windows Phone comes from Nokia in two forms. The various Nokia branded apps (Nokia Camera, Nokia Trailers, Nokia MixRadio, Nokia Creative Studio) and the HERE Suite of apps (HERE Maps, HERE Drive, HERE Transit). It'll be interesting to see what route Microsoft opts to take with these once its acquisition of Nokia's Devices & Services business is completed later this month.