Well there are certainly some TV's (or HD /cable boxes) that allow selection of audio line out as fixed or variable ( i.e. Sony for example) but that toggle can be buried 4 or 5 levels deep in menu selection
usually it'll be included near the option to turn off internal speakers; on the subject of which - when was the last time the onboard speakers / amps had any quality at all? I can remember the chip amp and bolt-on (APM?) speakers on my mid 80's XBR were "OK", but they were quickly bypassed.
My current system is an LG 42" plasma with sole source of Motorola HD/PVR (I've turned on the old school DVD only once or twice in the past 3 years), and Rotel RB850 power amp driving a single pair of DIY speakers, so it's simple to use the cable box's remote to operate the whole rig. While these (cable box) remotes are not universally intuitive or user friendly, once it and the TV's remote is used to program the input default and label settings, you can pull the batteries out of the latter.
Of course a full immersion multichannel HT rig with all flavors of input sources will be exponentially more complex control-wise. (doesn't there always seem to be at least one more remote required than the number of components in the system - you know to make it "simpler" to control?
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