Like I said, it's apocryphal and probably has other reasons (like the one you mention), but it's something you hear all the time about them to the point where it becomes major news and there has been some evidence presented, but as I said, it could just be newer versions of software requiring better hardware, which is still a bit iffy when you have an older phone and they want you to update to software that won't run as optimally on it. In some ways, Android actually benefits from this by just creating security patches for the life of the phone for the older version, and not updating to newer versions of Android like iOS does for old phones.