In the case of the HTC 8X, the decision was made by the maker of the phone itself. Vodafone Australia's software update page states, "HTC are no longer going ahead with this update." In the case of the Lumia 630, it's a different story, as the page says, "Issues found in testing. Nokia is no longer going ahead with this update." There's no word on what kinds of issues were found but this might just be a problem with the carrier and not with the phone itself.