I think what we'd be looking as is this: Take the cost of rendering the sequence in the first place. Now double it, because you're now rendering it twice, and odds are you won't
be able to just use the first version and add another rendering to make it 3D, you'll have to rerender the whole damn thing. Twice. Plus the cost of having to figure out how far to offset the one rendering from the other for the desired 3D effect, which'll be different for each shot (remember, these guys don't work for free, or even cheap), and like I said, even the inexpensive route costs major bucks. And all this for something that's still pretty iffy as far as the home market is concerned, and, as stated above, where there's no industry standard at present, which always invites disaster for at least one party (like the poor schmucks holding the HD-DVD bag), sometimes all parties (anybody remember AM Stereo?).
Network execs and studio heads are basically cowards. Nobody wants to be the first on anything, and generally won't make a move until someone else
neck out first.