Majority of Android tablets are rectangular with a black bezel, the Xoom and Viewsonic tablets are also similar in that respect. Apple just don't like the fact Samsung are actually beating them in terms of how thin and light the units are as it's one of Apples USPs that they've been plugging quite hard. They claimed the iPhone 4 was the thinnest phone in their tv adverts and the MacAir, well, that doesn't need explaining just by the name.
There's more to it then "rectangular with black bezel" and you know it.
Having spent an age in a three store today whilst sorting out my 4s contract (moving from a 3gs, so its a huge upgrade, before some of you call me a fanboy ) the only one which wasn't instantly recognisable as being "different" from a reasonable distance (8 feet or so) was the 10.1 tab.
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Other then the samsung logo, obviously
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I should also add, i was mildly annoyed at the fact that three kept pushing the SGS II down my throat, because to quote the worker "we have to do this because we earn more ourselves per device from Android handsets then Apple ones".