trying to use an unbiased eye

On friday, I had to take Thor and Buddha in for their respective check-ups. My Dr, who is just a cutie!, stated after hearing all of Buddha's many accomplishments(he's six months and crawling already!) "How Exciting this must be, but please, don't get me wrong, but you know that's just not normal, right?" And then there's Thor...
When You have a child, that child is born perfect, you have every aspiration for their life, and you know they are going to grow up and change the world. Heaven help the person who tells you that there is something not right, or norma, with that child. Thor has an AMAZING musical talent, one that we will nurture, support, and encourage. One that I tell him, at not-quite-two, is amazing. However, Thor is a little...well..I cannot think of a way to put it. He's stubborn? a perfectionist? manipulative? maybe the smartest of the three, maybe not? Thor has been delayed in his devolopment from a fairly early age. He didn't crawl when he was supposed to, but we were living with the in-laws at the time, including their two dogs and a cat, so we had an excuse. He didn't get as much floor time as we would've liked, and you cannot really crawl in a playpen now, can you? He was kinda late to walk. He would walk when he thought he wasn't being watched, and then only a little. We used his mortal fear of the vacuum against him, and by 18 months, he was walking like a pro, but still, much later than most kids. His speech is an entirely different matter. Sometimes he will speak in full sentances, or damn near, perfectly coherent and intelligable al day long, and then he will go for three days barely utterring a word. There are days where he will talk to innanimate objects, but he'll pointedly not utter a syllable for me. He is very affactionate, plays well, maintains eye contact, etc...so the Dr does not think it is autism, but she wants him to be evaluated to rule out any "issues". I am fine with his hearing test, honestly, but am scared shitless of seeing the "develpmental behaviorist" Two hour and a half long appointments, hopefully they will tell me his is fine, and just does things in his own way, and why the hell did my Dr send me, but when I look with as unbiased an eye as a parent can muster...I don't know. The uncertainty frightens me.