Messages launched with the original iPhone as "SMS", because that's all it did at the time. Apple had Safari, so they didn't build an old-school WAP browser and it turned out an old-school WAP browser is what MMS used and needed. So, Apple built one and, once carriers stopped freaking out about the potential bandwidth, added it to the app. Then Apple did an end-run and announced iMessage, integrated alongside MMS and SMS in the Messages app, and running on data completely outside carrier control. They brought it to iPad and Mac. Most recently, Apple enhanced group messaging, added instant sound-bites, selfies, and with SMS-relay brought the carriers to iPad and Mac as well.
Now we want to know what you'd like to see next? If Apple asked you what you wanted in Messages for iOS 9 and OS X 10.11, what would you tell them?