Group threads have been implemented as MMS on all major smartphone operating systems. Unfortunately, Android didn't get it until Android 4.2 or something.
The key is that the recipient list is sent with the message, so the other clients know who else is participating in the group, and can also thread and send outgoing messages accordingly.
Because you can send a message to a /person/ (or multiple people) instead of a /phone number/. Depending on said service, said person can interact with the message independent of device or phone number. Useful for people who interact with people who change phone numbers/devices often and/or travel between countries. Just send the message, and you don't have to think.
But people will forever stick to their stock messaging application as much as possible, sticking to slower, more restrictive technologies. MMS is a dinosaur.
or "Android device". technically speaking, "Android" should be "Android-based" for all devices that aren't pure Android, which may or may not be the case for the Moto X, depending on which Moto X you get.
I also think that /slightly/ adulterated stock Android might be "close enough" to count as "Android" instead of "Android-based", but I'm not sure.
The key is that the recipient list is sent with the message, so the other clients know who else is participating in the group, and can also thread and send outgoing messages accordingly.