Apple announced the original iPad on January 27, 2010, and the technology world hasn’t been the same since. Customers rushed to buy the tablet, snapping up more than 300,000 the day it went on sale. Competitors rushed to copy it, with Samsung, Motorola, Amazon, and others creating their own variations on the app-friendly touchscreen device within two years.

Equipped with a faster processor and a pair of cameras, Apple’s current model, the iPad 2, has sold even better than the original. And it still dominates the tablet category; as of Fall 2011, the iPad had grabbed nearly 70 percent of the market.

So why has the iPad proven so popular, even as competitors rush to put out their own imitations? One theory: combine a growing desire for Internet access and a shift to digital music, books, and video with a sophisticated, fast, lightweight touchscreen device, and you have a gadget perfectly suited to the emerging world of personal media devices.

You can add to that Apple’s new emphasis on the “post-PC” world, where you don’t have to connect the iPad to your computer to set it up, fill it up, or back it up. The arrival of iOS 5 and iCloud in October 2011 means that the iPad can be your primary window to the Internet for work, play, and cat videos—no heavy, bulky laptop needed, because you’re living in an airy ecosystem where all your stuff is safely online, Up There if you need it.

And thanks to the thousands of third-party apps already available, the iPad can move beyond being just a platter that serves up media and Internet content. In fact, it can pretty much be whatever you want it to be.

Come to think of it, that’s probably why it’s so popular.