You have a very strong point. Also, excellence can't be conjured into being just by throwing money at people and hoping they have the talent to do something useful for it. (Look at the VC-funded world; if the VCs could find a thousand people like me instead of the hucksters who currently run the show, they would. But it's just fundamentally hard to find great people.) The risks and especially the search costs involved in an excellence-based strategy are high and might be intolerable from an executive standpoint.
The good news is that what I said above is almost certainly right for a single actor. When you have this legacy oligopoly that has been treating some X as a commodity-- cutting costs, letting quality fall to the most manageable level (usually mediocrity)-- then, as that oligopoly loses hold due to technological change, a single player that takes an excellence strategy will have a good chance of making a big win, because the costs of excellence are not that much higher (a lot of the best shows, e.g. The Wire, started with no-name but talented actors) and the revenue potential is 10-100x (as with programming).
The bad news is that there may be a game-theoretic limit on the rewards of excellence. The fact that it works for one or a few players (e.g. AMC, HBO) might not mean that it scales. It might be that 5 players on an excellence-strategy dilute the benefits but pay the same costs. If that's the case, then this phenomenon is no better or worse than the 20th-century market's reward for branding. (While we associate the corporate-- McDonalds hamburgers, Hershey chocolate, Starbucks coffee-- withe mediocrity the truth is that most of these products were in the upper-middle tier of quality when introduced. They decline in relative terms because cheap, available, upper-middle-tier products kill everything below them and leave themselves at the bottom.) It may not be, at least specifically to TV, that an excellence strategy works for more than a small number of players (who'd become a new oligopoly).
However, I'm optimistic because the trend for software and technology is that the rewards for excellence strategies are nearly limitless (the scarcity of excellent people and ideas, not the "room" for them, is the limiting factor) and everything, including TV, is becoming a lot more technological over time.