I have three kids who all walked/crawled/rolled over at vastly different rates. My #3 (who is now almost 2 years old) really had NO interest in rolling over, crawling, walking. He just didn't want to, in my opinion! And with baby #3, I was happy to have a quiet, calm, non-mover! He didn't walk until probably 1 1/2 years old.
Our doctor also suggested physical therapy as well, which we did go to. It was useful in some aspects, but for the most part he did not need it. It was clear from observing the other children at the PT facility that he was not the average child needing PT; it was obvious to me that he would smooth out in his development with time. My feeling is that the doctor was young and wanted to make sure he didn't goof, which is good!
They did, however, teach me some little tricks to help him feeling more comfortable with his standing up from the floor (arising), his stance once he got standing, getting him to table walk, making him move towards a toy, etc. It would have been nice to say this helped, BUT they literally wanted me to follow him around all day making sure he was doing his stance/standing correctly - which I could not do because I work from home and needed to tend to work part of the time.
They did also evaluate him completely, and it was useful to see that his fine motor skills were ahead of his gross motor skills. For instance, he could pick up a Cheerio very easily - but just didn't like standing. That just made me feel even more certain that he was on a different track for development.
I would have to say in retrospect, that I was glad to have gone to PT with my child, because if there was anything wrong - we could have addressed it. I wouldn't want to be a mom who ignored the warning signs and failed to get proper care for my child.
Best of luck to you ~