Buzz Out Loud Lounge: Can someone explain this to me?

Can someone explain this to me?

Many of BOL podcasts talk about IPTV, Streaming TV / Movies, and Tom's delayed Apple TV. The question I have always hade is this: Television and movies, especially HDTV, have problems being played over the internet secondary to large file sizes and current broadband limitations. If this is true, how do I get HDTV broadcasts thru my cable now? Does a broadcast show use smaller file sizes when being sent to me via my cable service rather than thru the 'tubes' of my broadband connection? There seems to be such a large discrepency. I watch LOST in HDTV every week instantly on comcast cable when I turn my TV on, yet, if I wanted to download the same episode from iTunes (at a much lower resolution), it takes some time to dowload. I understand that a cable broadcast is more of a stream than a download, but even the movie stream services, such as Netflix, are no where near the resolution or smooth play of good ol' regular TV. I cannot seem to make sense of the extreme diference.

Sorry to be so long winded,

Greg from Michigan.