I agree with the recommendations to talk to the preschool staff, they know your son better than the doctor. Based on their recommendations you may want to see if you can get help for OT through the intermediate school district or through your health insurance. I look at it as any help they can get is good for them as long as it doesn't make them feel singled out or "bad".
My main reason for saying this is, a lot of the things they look for on these developmental lists, rely on practice. My son is 2 1/2 and has gross motor delays, and some of the fine motor stuff he didn't do yet because he hadn't had the opportunity to practice - we were always working on gross motor stuff. The same is true of speech. He hadn't passed certain milestones that "he" was focusing on, so he hadn't gotten to some of the speech tasks yet. Anyway, he is currently working with a teacher from the ISD for an hour a week. She is wonderful and has great suggestions for us to do with him at home. Same with the physical therapist he saw for a year and a half. Parent participation and cooperation and practice at home is crucial.
So if you can get help without breaking the bank or tying yourself in knots working out the schedule, I would say do it, but if not, the preschool teachers could probably suggest a lot of things to work on, on your own at home. The other moms had a lot of good suggestions that I have also been told to try.
"Don't worry, they all do things at their own pace" is one way to look at it - we were told that a lot with our son. But professionals who specialize in certain areas can tell you more about why it might help for your son to master these areas now. That is why we got help for our son when his deficits became clear. Then we wished we had done it sooner. He isn't handicapped at all, just behind enough that it was a grey area, like what you are seeing. So go with your gut, but it can't hurt to check things out.