Analysts have been arguing for ages about whether Apple (AAPL) is ever going to enter the $118 billion/year flat-screen TV market. But two things have changed in the past month:

1. Walter Isaacson’s biography of Steve Jobs quotes him as saying he’s “finally cracked” the problem of controlling an integrated cloud-based television.
2. The Siri system that Apple introduced on the iPhone 4S seems custom-made for replacing most of the remotes in the house with a simple voice-activated assistant. Just ask it to turn on the Yankees-Red Sox game, and you’re in business.

It’s in this context that Sanford Bernstein’s Toni Sacconaghi issued a note to clients Friday to address the possibility.

Bottom line: He ran the numbers, and they just don’t work.

“The television-viewing experience appears ripe for innovation and Apple has the technology ingredients to do so,” he writes…

“That said, we wonder if Apple’s aspiration to revolutionize television might be better served by selling a consumer-electronics box – i.e. Apple TV 3.0 – instead of a full-fledged integrated television. Specifically, we note that the while the global flat-panel television market is large ($112B in 2012E revenues), it is forecast to decline overall, and has historically had low profitability. Moreover, virtually all of the benefits that we have outlined can be delivered by selling a box that connects with a user’s existing television. In fact setup and operations would work the same for an iTV vs. Apple TV 3.0 box.”

The way he sees it, even if Apple could secure the necessary content rights (a big if), it would still have to fight hard to grab a 3% share (about 8 million units) of the flat panel TV market. It could make as much money, Sacconaghi says, selling three times as many Apple TV boxes at one sixth the price.

He may be right. If so, let’s hope the set up is less complicated than the one pictured in Sacconaghi’s diagram, above.