At&t didn't give us the software apple did, at&t just had apple hold back the correct carrier file until they were ready. Apple is still very new to the phone industry and you have to admit for the iphone only being a little over 3 years old it is doing very well. And for only having added mms this past year they did a pretty good job. I'm sure their first concerns were that the media the iphone could take (pictures and video) with it's camera was supported over mms, now they will work on everything else. It's up to apple to support it with the software. I am sure apple has received feedback about it and will release a patch to deal with it. If it was at&t's fault you wouldn't have even received the animated picture(not sure exactly what they are called).
You can send feedback to let apple know about it
http://www.apple.com/feedback/iphone.html