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For the past 2 1/2 years, iPad as has ruled the world of tablets. Except for Amazon’s Kindle Fire and the Barnes & Noble NOOK Tablet, both special-purpose devices dedicated to consumption, there has been no competition worth mentioning. But with the entry of Microsoft into the fray, both with the Surface and an assortment of third-party Windows 8 and Windows RT tablets, the business is about to get a lot more interesting.

I start from the premise that only competition keeps the tech business driving forward and that in the absence of effective competition products stultify. This definitely happened in PCs. After Apple failed to respond to the introduction of Windows 95, the Mac market share fell to the low single digits and without effective competition,...