I live near Philly and I have a crawl in my 'suburban home'. Yes, some homes in some parts of the country do close off their crawls. I think those places are in warmer climates and they do so for a very short time. This is because their floors and pipes aren't insulated under the crawl, and it's what they must do to prevent their pipes from freezing during an unexpected, deep or prolonged cold spell.
HOWEVER, I don't think you have a problem. 1) If your floor is insulated as well as your pipes, then you SHOULD be OK. 2) What are your neighbors doing? 3) What does the former Owner say??? If you can get ahold of your Home Inspector, I'd talk w/him. He should have 'noted' if the floor and plumbing was insulated, and should be able to 'guide' you.