Group texts may not be as simple as you think... What may Android users don't realize is, many of the "interface" features are not part of the stock OS but is part of the Skin that the handset manufacturer or the wireless provider put on it. I have been told that the newer versions of Android (Jellybean for instance) has more functionality so these "skins" aren't as heavy duty. Also many manufacturers take insult to the term "skin" because of the amount of development and changes they make to the functionality of the Android OS. This is not a good or bad thing, this is just the nature of Android.
That being said, let's talk about iMessage vs SMS. iMessage is a service that Apple created to allow iPhones, other apple devices and Macs to talk to each other. When an iPhone user is sending an iMessage, their "send" button is in blue. If an iPhone user is sending to a non-apple supported device, it automatically uses SMS and the "send" button turns green. When sending a group message, if any one recipient in the list is a non-apple device, the whole message is sent using SMS (green button).
I have found that some Android phones receive these messages find and some don't (again because of the effort made by the manufacturer). But before you blame Apple or AT&T, I have seen them have the same issue regardless of carrier or device. I have friends with iPhones on multiple carriers and I have friends with Android phones and Blackberries and other types of devices. It's only certain manufacturers of some Android phones that seem to not support this group messaging.
The reason why I am on this site, is because I was hoping to find a solution for one of my friends who can't participate in the group texting... it sounds like there may be a few 3rd party apps that she can try out. Since my other Android friends don't have this issue, we know it's just a limitation of her handset.