DS7 is 2E with Aspergers and completely lacks any registering of social hierarchy. He will correct ANYONE not because he is being mean or disrespectful but because, in his mind, if something is wrong it should be corrected. He will also states things similar to what your son did because he sees them as just a fact. With DS we work on an ongoing basis to explain social hierarchies to him and to explain why some things are best left unsaid or uncorrected.
I don't know what your son's background is but I would see this more as his limited understanding of the world than an outright show of disrespect. If you think about his perspective, it probably seems to him that the baby isn't getting much use out of the speech therapy-if she was then why wasn't she talking yet? And, as for the doctor's visit, I have certainly left doctor's appointments wondering if the visit had truly been worth my time and money so I wouldn't be surprised if my son wondered that at some point as well. The only difference is an understanding of what are largely unspoken rules of social order. These rules don't come naturally for some kids and that's where we have to step in and explain them.
