On average, investors attempt to visualize the trends 12 to 18 months out. Apple's policy of not commenting on future products or strategies has the downside effect of leaving investors and end users with little guidance on how the company plans to cope with new challenges. Normally, this isn't much of a problem because the PC industry evolves incrementally. The next step is usually fairly obvious. But today the industry is faced with a radical design challenge brought about by the ubiquity of the Internet and steady advances in electronic component miniaturization.
People invest based on their expectations for the future.
Once consumers grok that prosperity isn't likely to slip out from under Greenspan's thumb they'll cut back on their purchases of all things not entirely necessary, including iMacs and iBooks. Or so goes the conventional wisdom, but we won't digress into the macro-woes of the equity markets. Suffice it to say the stock market has the flu. However, Apple is more than a company, it's an entire platform. Even more than that, Apple is a philosophy about how humans should interact with machines.