Comcast has been dropping Weatherscan over the past year. As for MHZ Worldview, that is a broadcast network carried by a local TV station, usually PBS. Most likely, the station dropped it. Comcast has no control over that.
If you are in the DC area, I also saw this:
Also, in the Chicago area, after WYCC went off the air, WTTW decided to pick it up. It will resume April 23 on Comcast 372, or broadcast 20.1 (which will actually be a WTTW subchannel.)