Asymco‘s Horace Dediu spent much a recent trip to London talking to dozens of buy-side analysts. Not to be confused with sell-side analysts, these are people who control trillions of investment dollars and never share their thoughts or strategies in notes to clients.

He came out of those meetings convinced that the investment thesis of the funds that control 70% of Apple’s (AAPL) shares is that the company is a sum of its current product line and nothing more.

The stock went up in 2005 when the iPod was hot and fell in 2006 when it looked like sales were fading. It rose in 2007 on the promise of the iPhone and collapsed in 2008 and 2009.

“Throughout this volatile period,” Dediu wrote Monday in a post entitled Is Innovation Valuable, “the investment thesis remained fairly constant: Apple is a rather small collection of product bets. Owning Apple meant riding the iPod or the iPhone or the iPad as waves of growth. As soon as one growth wave was seen to start to fade, investors would say the same thing: Apple is done.”

“What intrigues me about this investment thesis,” he writes, “is not whether the signals of growth are interpreted correctly or not, but rather that an investor in Apple in 2006 was considered perfectly rational valuing Apple as an iPod company as much as an investor today is perfectly rational valuing Apple as an iPhone company. Why would anyone buy Apple for any other reason? There is no evidence that Apple can be anything more. Any fund manager positing a different point of view would surely be limiting her credibility.”

Looking at Apple this way, he says, is like valuing Pixar on the box office sales of its current movie — as if the studio weren’t a hit-making machine.

“Until and unless an explanation is available that persuades a majority that Apple is as much a hit factory as Pixar,” Dediu concludes, “then Apple without the products will intrinsically be valued at zero.”