In a 'Fun fact' tweet he posted yesterday, Margolis points out that the new UI designs were actually tossed out five years ago because Steve Jobs didn't like them. But now that Jobs has passed, there's no one at Apple to say "no" to bad design.
However, in the comments section of another post about the tweet over on The Next Web, Margolis later clarified what elements in the UI Jobs specifically didn't like, and conceded that the updates are probably a smart move to bring the Apple TV UI more in line with the company's popular iOS products:
The new UI shouldn't come as a surprise to anyone. There is a clear effort at Apple to make everything match the look and feel of their popular iOS products – starting with Lion and increasing momentum with Mountain Lion.
To be clear – he didn't like the original grid. This was before the iPhone was popular and before the iPad even existed.
Given that the iPad is far more successful than the AppleTV, migrating the AppleTV to look more like the iPad was probably a very smart move – even if some of the users of the old UI don't prefer the new one.