Beginning last summer, Bungie and 343 Industries began transitioning Halo data and services, in preparation for Bungie's departure into an unknown future with Activision.
That transition process is set to be completed this spring, on March 31. At that point, all Halo related goodness will be handled by 343i, the studio responsible for developing Halo Waypoint, plus Halo CE Anniversary and the upcoming Halo 4.
Bungie did promise to "preserve all existing historical Halo data on Bungie.net for as long as the Internet and Bungie's data storage systems remain functional." Because they love their fans as much as their fans love them.