The difference appears to be an "Rear active diff" versus a locking diff. Most 4x4s (my Rubicon as an example) simply have locking diffs, which works pretty well. Granted the "active diff" is likely an improvement but a 2012 without the HD package would appear to be significantly more off road capable than a '14 or '15 without the HD package.
That info from Motor Trend is bogus. No LR4, regardless of model year - except perhaps some limited edition, not sure - ever came standard with a locking rear differential as part of any trim (HSE, HSE Lux) unless fitted with the extra cost Heavy Duty package, which up to MY13 used to include the full size spare as well.
As of 2014, the HD pack also includes a 2-speed transfer case, which used to be standard in the LR4 up to MY13. Because a Terrain Response program (Rock Crawl) only engages in Low Range, that program is removed from the Terrain Response selections of MY14+ with a single speed transfer case and no Heavy Duty pack.
As far as different "flavors" of rear differentials, Land Rover only makes 2: an open / non locking rear diff (standard issue) and a locking one. "Active", "Electronic", "Electronically Controlled", etc., are all used to describe the same locking diff, which is indeed automatically activated as needed, without any input required from the driver.
