I love iOS but I completely agree that this is a sorely missed feature. Despite being able to go into the photos app and copy/paste into the message, it's a complete p.i.t.a. Other apps have access to the photos app there is absolutely no reason why apple can't make this happen.
Especially with the lack of MMS when the iPhone first came out and said people can just email pictures etc, this should have been baked into the OS from Day 1.
Agreed. All they need is to add the option to the Action button.