Just like what happened with the iPod and iPod Touch, right?
Consumers don't all want to own the same smart phone, in fact quite the opposite: consumers are completely unwilling to all own the same smart phone.
Then to top it off, the smart phone market is roughly 20 to 30 times larger than the iPod market. Which means a helluva lot more competition. There's also no simple blocking method available to Apple to own the smart phone market, unlike the iTunes + music licensing moat they had in music players.
The iPod had a moat around it courtesy of the extremely difficult dynamics of dealing with the music cartels. Apple broke the cartels and came to dominate them; nobody else was able to. Such problems don't exist in either smart phones or tablets.
"In reality, 2012 will be the year the iPad loses its market dominance in tablets. By the end of 2013, Apple will hold 1/4 to 1/3 of the market, which is exactly what their entire business model is designed around: lower market share, much higher margins."