I don't think anyone ever really says that general education teachers don't really have to teach everyone but that is certainly implied by the dual educational system we have. If there are special ed teachers then they must be the ones who are responsible for special education students, right? So as we all move towards inclusion, as long as there are still special educators the message will still be the same- not all kids are "right" for general education. This message is received by teachers, students, parents and administrators alike- so everyone's on the same page: the wrong one.
As long as this dual education system continues inclusion of special education students will come with an implied caveat that goes something like this: "This disabled student can be in the general education classroom as long as she acts relatively normal and doesn't force me to move out of my comfort zone." "Looking normal" would be something like not behaving or performing substantially worse than the "average" student. A teacher's comfort zone would include the behaviors she can deal with and the accommodations she is willing to make. If these conditions aren't met then the disabled student "just isn't ready yet."
So if I could, I would tell all educational professionals that we have a responsibility to educate everyone who walks in our doors. In fact, that really needs to be said to pre-professionals and then repeated every year until retirement. The problem is that I could say that with words, bu the institution of special ed, by it's very existence, tells them that I'm wrong. Bit of a sticky wicket. So what all professionals should know is that is that a) we have a dual education system and b) this system is unfair primarily to people with disabilities as secondarily to all of us.
Finally, all professionals should know that it doesn't have to be this way.