The Galaxy S3 has a different microUSB port than other Android devices, as the port’s pins have been rearranged. That means the Galaxy S3 will not work with standard MHL (Mobile High-definition Link) adapters, which let users connect smartphones that come with microUSB ports to big-screen TVs.
Whilst not as dramatic a change as the 30-pin to Lightning, I don’t see how this is much different than Apple changing their (almost 10 year old) connector. Unlike Apple who’s reasons were that the 30-pin connector is simply it’s just too old, large and cumbersome to remain viable without holding back innovation, Samsung’s modified microUSB connector has no physical change other than the pins are different.
Whilst previous charging cables would no doubt still work with the S3 (the power pins are the same), you do get a new USB charging cable with the iPhone 5 and new iPods.