Really all TV (OTA or cable) in the US is delivered at 1080i or 720p.
I'm sure all these shows are shot on digital at 1080p though, and you can get that from download services or Netflix.
Yeah, definitely. Some CW affiliates broadcast as low as 480i (
depending on whether they're in a market where they are broadcast as one of a few subchannels), with 720p and 1080i being more common (depending on whether they are the secondary subchannel or the main channel on a feed respectively).
This of course is leaving out the more important bits: what bit-rate the video is broadcast at.
My CW, for example, is the main feed on a stream with 2 channels (the main 1080i CW feed and a 480i feed for a game show network). Those two channels have about 20mbits/s to share on their feed. The CW gets the higher allotment, roughly 15mbits (~2MB/s) or so, and the gameshow feed is set to be variable, but for the sake of discussion, let's say it takes no more than 5mbits (~500KB/s). This is important as this is what is re-transmitted by my local cable companies, Comcast and Verizon Fios. Verizon re-transmits an exact copy of the over the air signal I pick up from the antenna because their network is newer and has more bandwidth available to it. While I don't know what Comcast does in my area, they often have to compress their feeds to fit the number of channels they have to deliver, which would theoretically be worse than my OTA signal.
Okay, home stretch: the bitrates for the shows downloaded from iTunes and Amazon are most likely even higher than the bitrates I've mentioned so far. So, for example, I believe a 1080p episode of the Flash is approximately 44mbits (~5mb) a second, or effectively double the bitrate of a broadcast signal. This does not take into account the codecs used on iTunes, as broadcast TV is usually transmitted in MPEG2.