I think I can see what you're getting at and this is by no means a complete answer, but here's something to be going on with.
IMHO, while it's certainly possible in principle to set up various equipments exactly as you envisage, there are (currently) various practical factors and limitations to take into account, and which unavoidably complicate the overall issue.
Just one example, a Sky digibox can output high-quality RGB video to a DVD recorder and to a TV - but currently there's no convenient/inexpensive way of getting RGB into a computer. So you have necessarily to fall back on using the much lesser-quality composite video.
Similarly, computer monitors aren't primarily designed to display TV progs or video (including high-definition). It is possible to do so, but it ain't convenient and there are unavoidable limitations. For example, a 'widescreen' TV is 1.77:1 aspect ratio, but a widescreen computer monitor is 1.6:1, so cannot fully display a 16:9 TV/video display.
And while in principle it's possible to record TV progs onto a computer's hard disc, strteaming that around the house is by no means a simple project.
In other words, it's a whole series of working compromises which, when taken together, create far more problems than they solve. Sadly, it has to be accepted that, for all talk of 'Media Centres' and all-in-one solutions, "received wisdom" (as discussed in these forum pages) is that we haven't yet reached the stage where one size fits all.
Domestic audio-video units, e.g. a Sky digibox, stand-alone HDD/DVD recorder and a posh TV, maybe with internal Freeview tuner(s), are designed to work well with each other, regardless of manufacturer. But for all sorts of reasons, they ain't (yet) designed to integrate with a computer and monitor.
No doubt the time will come - my guess is not less than 3-5 years.