Is there any one place to view the technical specifications for the major cable channels and networks, i.e. what do the Discovery Channel networks, PBS, etc, require from producers submitting work. Camera codecs, etc. I know you visit each channel website for their respective specs, but I wondering if they all reside in one place.
I don't know of any place that has everything together.
However, there is a lot in common between broadcasters, they're all pretty much the same for Rec.709 video levels, camera codecs vary a bit (50MBPS is almost always fine, 35MBPS is frequently fine but sometimes not, anything less than 35MBPS might be ok but you can't assume it will), and there are different ways of measuring audio levels (loudness or absolute levels).
Safe title areas are probably the most variable, some broadcasters specify narrower areas than others to account for the way they handle analogue SD transmissions or to avoid subtitles clashing with channel tickers/ idents (I know of one broadcaster which had an unusual safe title area requirement last year, this year they're specifying no titles on the programme you supply, you need to supply a list and they'll do the subtitling themselves).