My cable box shows HDTV and the resolution.
As does every cable box or HDTV. Doesn't mean squat, really. Last year most network channels only broadcast HD shows after 8 p.m. or so. The channels still list as 720 or 1080 before then, because they're broadcasting a 720 or 1080 signal. The source going into that signal however wasn't HD.
For example, tonight on NBC, channel 11.1 I have news at 6, which is broadcast in HD, NBC nighly news which is HD, then inside edition which is SD. The TV will still show 1080i however when Inside Edition comes on.
CNN uses 16:9, but the actual video is in 4:3 in the center of the screen with a filler on either side.
Yes, when they are using their SD cameras they put CNN on the sides to fill out the screen. Compare how it looks to the shows they shoot with their HD cameras, there is a huge difference in quality.
actually 720p since it is far superior to the 480i
That'll vary channel to channel, it all depends on the processing equipment and software they're using to put out the signal. Same thing here, one or two of the network channels looks good on the digital channel when the show is standard def, a few others look worse than viewing the analog signal.
Not unlike how some upconvert players make a standard def DVD look great on an HDTV, and some leave a lot to be desired.