Good luck with the developmental ped. I haven't seen one but just wanted to say I HEAR YOU and you're absolutely right. As is PP. There is NO REASON to wait. That's terrible advice, often (not always) given by people who aren't capable of recognizing potential problems in children under 3 in the first place.
We got the wait advice from 2 pediatricians, one of whom was supposedly an expert in development. (He wasn't, however, a "developmental ped"--I didn't know to look for that.) We went to the EI clinic at the local hospital anyway. They found gross motor delays and recommended PT. Unfortunately, they missed the rest of what was going on with my baby. After he graduated from PT and caught up on motor milestones I still wasn't satisfied. I finally saw someone (once I found her it was NOT a long wait to see her) who could see what was going on and believes in addressing issues while babies brains are still growing. She's a developmental psychologist.
She said that parents who have concerns are almost always right. Yes, some people look for trouble that isn't there but the vast majority aren't nuts. We may not know what it is (though given your background you probably do know what it could be), we're responding to "something" that turns out to be an issue.
We've gotten great help--referrals to OT and speech--and feel like we're on the right track with DS.
I hope you have good luck with this developmental ped.
If you aren't satisfied with the conversation, you might check this web site. Actually you might check it out anyway for therapists, if you end up needing them, regardless. These folks are trained in a model that encourages earliest possible intervention. It may be too soon for a formal dx but that doesn't mean you can't address the concerns. Dr. Stanley Greenspan, former NIH official and big 0 to 3 advocate, started this group.
http://www.icdl.com/
Hang in there. Your son is very lucky to have such a persistent mama.