"Most of the devices in the market are competing with the iPad based on hardware features," Gartner analyst last year, "and hardware is a minimal part of the equation."

Software, on the other hand, play a defining role, Baker says. Apple boasts some 400,000 iOS apps lining the shelves of its virtual App Store. Android's app stores are growing by leaps and bounds every day.

And that's just the beginning, according to market researcher Forrester. A new Forrester report predicts the combined spend on apps and services will be $54.6 billion a year by 2015. (Check out our top .)

A Forrester survey in January showed that the average iPad owner downloaded 20 apps and spent $34 on apps. Half of iPad owners said they use the devices to read newspapers and magazines. Sixty-three percent of the money consumers spend on content of all types comes through a renewable subscription, writes Forrester analyst .

All of which bring us back to Apple's crucial in-app subscription service. Here are three very big reasons why the move is a bad one: